How do i deal with missing school?

i am in all pre ap 2 cles at school except for history and im the only one student allowed to take out a computer. my problem is that i am new here and just got through 1/2 a semester last year as a freshman. the twist is that this school has a weird routine. they have A day and B day. i am having a hard time adjusting. i fit in with the crowd and have friends get very good grades but cant handle the stress! i am falling apart! i am litteraly getting sick by stressing out too much. some and most days i have to stay up the entire night and proceed to stay awake in all cles just like im doing now. my problem is that i was sick for 2 school days one week and then 1 day the next and went to school the next day. i missed 2 B days and 1 A day. and the rest of this week of thanksgiving just ped. i had no way of contacting most of my teachers and on the last day that i was at school i couldnt stay after school because of the holidays and i couldnt get any extra info on any of my homework. (btw i spend all of my time after school for about 2 hours every day and my lunches as well) all of my rescources were worthless and now i am struggling to finish. i was sick the days absent but in a few days i have to leave overseas for another week i dont know what im going to do! i need help and the reason i spend so long at school is because of my ADHD and i do take meds for it but still they are ineffective no matter what the dosage. yes im focused but i cant concentrate... basically im stress about what is to come, my grades, and how im going to get through all of it and still make an A B average :'(