I felt really down then unusually happy, dependng on where i am. bipolar?

Maybe...: But there's more to it than that. If you are struggling with your moods, there is a need to get help -- and there is plenty of help available to you. Start by talking with someone calm, caring and helpful -- someone you know whom you respect, and who respects you. Progress to professional help, unless everything works out fairly quickly.

Bipolar: This sounds more like rapid cycling. May need to rule out hormonal changes, vs. Medication-induced vs. Agitated depression.

Don't know: We all have variability in our mood. It sounds like you know what is tied to your changes in mood. If mood changes are significant then psychiatric evaluation would be warranted. I wouldn't try to diagnose you with the available information.