My period won't go away!

I get my period about every 2 1/2 weeks and it lasts around 10 days. I went to the doctor and they did a bunch of tests and said that it isn't fibroids or endometriosis or anything like that, that I'm probably just having break through bleeding because I'm getting used to my birth control pill. So they switched me to a different pill. That worked for a month and it is progressively getting worse. I keep asking the doctors if it could be a medication interaction, because this new medicine I'm on (Nuvigil for narcolepsy) says it can interact with birth control. The doctors say that's not what it is. I went back and got a pap and that was normal but they said I had a yeast infection and gave me meds (like a month ago).

I'm not bleeding the whole time, it stops and starts. I haven't been having it at night at all, and the flow is all varied. Sometimes it is light spotting other times it is heavy. It's been starting and stopping for the past 8 days, just when I think it is over it starts up again.

I'm thinking maybe I should stop taking the birth control (I just take it for PMDD and heavy periods). But I'm worried if it lasts this long ON the birth control how long will it last without? I started taking 4 years ago because I have really heavy periods and extreme cramps and mood swings.

Oh and I take my birth control pill at the exact same time every night, and the medicine that could be interacting with it I take in the mornings.

Are there any things I should ask my doctor to check for? Hormone levels or something? I'm getting fed up with this.