Have you talked about your concerns? Generally a lack of sex is only a symptom of a greater problem that needs addressing, and that's what has to be figured out.
Where does he get his pot money from, and why doesn't he work? Don't know the meds he takes, but you can Google them for side effects but a doctor would be the way to go.
Also what has changed, or made circumstances different such as arguments, or disagreements that have led to resentments, or unresolved conflicts.
With you working, and in school, is your expectations of attention from him to high? Hard to say what's going on between you, but you both should be talking.