I had this problem shortly after getting our apartment. The people below us moved out and smokers moved in. And I know smoking is allowed in our apartment building (just not common areas). Well, I called the landlord anyways and he said they're only allowed to smoke inside if it's not bothering anyone else. When I complained to him, he said he would take care of it. It did get a lot better, but I'm pretty sure they got evicted a few months later anyways.

So, honestly? I would talk to your landlord first. Then if there's nothing he can do, you can go talk to your neighbors. Lastly, I'd probably start looking for a new apartment. If you're worried about wasting money -- you already wasted money having to drop a class because of this. Don't waste any more by staying in a place that makes you miserable and damages your health and could lead to even more money down the drain in doctor bills, school bills, unnecessary heating bills....