Women advice/ help please.?

I have had an IUD in for about a year and a half and I have been getting vaginosis every month it seems like. I have no STD's or HIV, and have been cleared by my doctor. I told her I get yeast infections or vaginois all the time and creams dont work. She put me on this pill thing where I take one every 3 days and their was only like 2 pills and that didn't work. I am wondering if it could be my IUD. I have been with the same person for over 5 years and the same for him. NO STD's so what the hell?Women advice/ help please.?
I don't have a IUD, but also have started to have constant vaginosis. Mine is not really bad, but the medication is not working for me either. There are several reasons why you get bacterial infections. It occurs when the ph in your vagina is disrupted. If you are having unprotected sex and your partner is ejaculating inside you, this could be why. This is what set mine off, and can't get it back to normal even though he hasn't done it since. I was also told that sometimes once you get one, you can be prone to getting them more often. Other women have said that they have had reoccuring infections for a few years and then just cleared up on their own.