During my chemo I had problems with that, and diarhea. I would get one, then get that fixed only to go too far the otehr way. Docs would give me meds to make me go, then I would have to take something else to make me stop. Seems there was no inbetween. I would tell your Doc, they have meds that will work, they just need to know your having a problem and they will help you with it.
Hope it works for you, I know it's miserable.