My daughter has been really distraught lately and is throwing tantrums for no reason. I have tried everything, but nothing seems to be working out. I don’t know what to do.
The first thing to understand is that there actually IS a reason even if you can’t see it 
Kids that age don’t have the words to explain what they are feeling so it just comes out as screaming and crying. Could be she’s overtired, hungry, overstimulated, or frustrated about something completely different than what you think. What helped me was trying to stay calm and just let it happen without making it a bigger deal. Like don’t try to reason with her in the moment because that never works when they are already worked up. Just make sure she’s safe and let her get it out of her system.
Been there and I feel for you. It’s exhausting when every little thing sets them off 
My son went through this phase last year and what finally worked was figuring out his triggers. Turned out most of his meltdowns happened right before lunch or when he was tired. Once I started giving him snacks earlier and making sure he got enough sleep the tantrums dropped like 80 percent.
Also I stopped saying no to everything. Picked my battles you know? If he wanted to wear his superhero costume to the grocery store whatever. Not worth the fight. Save the nos for stuff that actually matters like safety or being mean to others.
Okay so this might sound weird but tantrums are actually developmentally normal? Like it’s how kids learn to deal with big emotions 
Instead of trying to stop them completely maybe focus on how YOU react to them. If you stay calm and don’t get angry or frustrated then they learn that emotions are okay and can be managed. If you freak out too then it just makes everything worse.
Not to be that person but have you checked if something changed recently? 
Kids are way more sensitive to changes than we realize. New school, different schedule, family stuff, even just rearranging furniture can throw them off. My daughter had a meltdown phase when we moved her to a different bedroom and we didn’t even connect the dots at first.
Also screen time can make tantrums worse. Something about how it affects their brain or whatever. We cut back on tablets and TV and things got better pretty quick. Might be worth trying for a week or two and see if it helps.
This happened with my nephew and what his parents did was give him choices instead of just telling him what to do 
Like instead of time for bed they’d say do you want to brush teeth first or put on pajamas first. Still gets the same result but he feels like he has some say in it. Tantrums went way down because he wasn’t fighting for independence all the time.
Obviously doesn’t work for everything but it helped a lot with the daily routine stuff that was causing most of the drama.
Has she started a new daycare or preschool recently? That was the issue for us 
My son was fine until he started preschool then suddenly tantrum city. Turns out he was holding it together all day at school and then just falling apart at home because that’s his safe space. Teacher said it’s super common - they call it afterschool restraint collapse or something.
Once we knew that was the cause we just made sure to have quiet time right after pickup. No errands, no activities, just home and chill time. Made a huge difference. He still had tantrums but way less intense and he’d recover faster.
Look I’m gonna be straight with you sometimes kids are just going through a phase and you gotta ride it out 
My daughter turned into a complete nightmare around 3 years old. Screaming over the wrong color cup, melting down because her sandwich was cut wrong, the works. We tried everything and nothing really fixed it. Then one day she just kinda grew out of it.
That said you still need strategies to survive it. What worked for us was warning her before transitions. Like in 5 minutes we are leaving the park instead of just grabbing her and going. Gave her time to mentally prepare I guess. Also having a calm down corner with books and stuffed animals where she could go when she was upset.
The staying calm part is the hardest thing honestly…
When my kid is screaming in the middle of Target I want to scream too. But I read somewhere that you can’t pour from an empty cup or whatever that saying is. If you are burnt out and stressed then dealing with tantrums becomes impossible. 
Make sure you’re taking care of yourself. Get breaks when you can. Ask your partner or a family member to watch her so you can just breathe for an hour. When you’re less stressed you’ll handle the tantrums better and she’ll probably pick up on that calmer energy too.
Something nobody talks about enough, what if there’s an actual medical reason? 
Not trying to scare you but my friend’s daughter was having constant meltdowns and it turned out she had an ear infection that wasn’t obvious. She was in pain but couldn’t explain it so she just cried about everything. Got treated and boom back to normal.
Also food sensitivities can cause behavior issues. Might be worth keeping a food diary and seeing if tantrums happen more after certain meals. Could be something like red dye or too much sugar messing with her system.
Just something to consider if nothing else is working. Sometimes it’s not behavioral at all.