Where wild minds come to rest
Place yourself in reality as much as possible. If you have to do homework go somewhere public where there are alot of people so its harder to escape. Also get involved in things that force you to interact heavily with people like sports or a club, this will distract you from falling into the MD.
Getting rid of the triggers is a good start. TBH one of my biggest triggers is music but I can't get rid of it because it also is my saving grace during anxiety attacks, but i've realized that by listening to music without headphones makes me less likely to go into that state. My md episodes are really only harmful when i'm having an extistental anxiety phase because it helps me not think about reality and I usually escape to my room. Do not go into isolation if you feel a bad MD episode coming on because going into your room will just want to stay there and there is nothing to pull you out of it.
Honestly I believe that if you can find something within reality that you really enjoy and keeps you active I think the severity of the MD will go away and it wont be so restraining anymore.
Like other people have said, exercise is really good. Try and avoid triggers, though I know it's a constant mental battle. It looks like you have got yourself caught in a loop - after all day dreaming is often a coping mechanism that is running out of control. You really need to talk to someone about this, is your family sympathetic? You don't need to go into detail about the daydreaming, but say you're struggling and feeling really lonely and low. I found opening up to people helped me a lot, I didn't talk about daydreaming but I said how depressed I was, and just admitting it kind of turned a corner. I remember a friend asking me if I was ok, and I just sat and cried and cried for about an hour, such a relief admitting finally that no, I was not ok, that this was not how I wanted to be.
Try to sit downstairs with your family a little more, or alternatively sit in a coffee shop or something, you don't need to talk to people but sometimes just being in the company of others helps. Personally I've found Podcasts help hugely because basically if I'm listening to a podcast I can't daydream! I'm forced to concentrate which is good for me. I've found yoga good too.
Does your College/School have a counselling service? They would be willing to help you, a lot of people your age struggle with school and it's awful feeling isolated. Alternatively is there a sympathetic teacher you can talk to?
You must be kind to yourself and tell yourself this is a phase you're going through and you will pull out of it. Its rubbish I know, 6 months ago I was an obsessive daydreamer but lately I've been improving. I really hope things improve for you :)