I agree that it would be a good idea to get a medication to take as needed; that way as you just start feeling like you're heading towards mania (before you're entirely delusional) you can take it and hopefully come down.

I would also try to get a second opinion in order to get a diagnosis; symptoms help inform treatment, but I think that -long term- a diagnosis would be helpful for your treatment.

My pdoc told me once (and she specializes in BP) that she has patients who go for 10 years without an episode, so you're not alone in having long periods of health between episodes.

This is assuming you have BP, but I would really get a second opinion from a pdoc who is willing to give you a diagnosis.