2) I find it pretty unlikely that your parents could observe a bona fide manic episode and have any doubts. It is, as you may know, quite striking.
It's possible to be bipolar without ever having a full manic episode. It's called bipolar II and you have hypomanic episodes that aren't very healthy and do interfere with your functioning but aren't nearly as debilitating as manic episodes. If the OP hasn't lived with his parents since the onset of his bipolar or his parents chalk up the symptoms of the hypomanic episode to other things like being busy with schoolwork and suffering from anxiety and stress (like agitated mood, not sleeping for a few nights, talking too much) it's entirely possible he has bipolar II without his parents knowing.
The last meeting I had with a psychiatrist she wasn't sure whether I was just generally depressed or had bipolar II. I think it was the latter, but at the time I was terrified of the side effects of mood stabilizers so I never followed through and got medicated for it. I can function fine if I keep in mind some basic things:
1) Exercise -- getting my energy out this way helps keep me from feeling too agitated and helps me sleep
2) Sleep -- sleep deprivation can bring on hypomanic episodes. When I was a freshman I noticed that if I pulled one all-nighter it felt addicting and I'd wind up staying up for like 3 days working on homework and cleaning my apartment. Good for the GPA, bad for your health. I can still pull the occasional late night, I just make sure to take a nap or go to bed early the next day and not let the sleep deprivation accumulate.
3) Sunlight -- it makes me happier, and getting some early in the morning can help you sleep at night. It's good for anyone who is depressed too.
4) Nutrition -- I feel sleepy and depressed if I eat too much sugar or empty carbs, and I think too much caffeine can bring on hypomanic symptoms.
5) Alcohol -- unless you're on certain medications, you can probably drink. Just don't drink too much. The recommendations for women are 1-2 a day, slightly higher for men.
6) Social life -- Being around other people keeps me from getting too depressed. But I do tend to party really hard when I go to a party (not just drinking too much, I tend to be the last one awake, to not want to leave and go to sleep) so I can't do that too often.
This isn't medical advice. This is just what works for me combined with what I've learned in my psych classes. Obviously listen to your psychiatrist above everyone, but basic wellness things like exercise, sleep, sunlight, and good nutrition are more important for you if you have a mood disorder than they are for the general population. If I keep a good lifestyle I notice that my disorder only interferes with my grades in the sense that if it comes between sleep and homework, I need to pick sleep. This dilemma can be avoided with good time-management though. I know I'll struggle for the balance sometimes in med school, but I figure if I pick a specialty with a decent residency lifestyle (I'm thinking of psych or EM) and manage my time especially well, it'll only be a major struggle during the worst rotations of med school and residency. Hope that helps somewhat!