vaginapagina | Keeper causing YI and what to do

Sooo I have what appears to be my fourth yeast infection since February. The first one was random, the second one was triggered by anti-biotics, the third I SUSPECT was from my Keeper cup, and now I really do think it's the Keeper because I have the Ominous Itch & Irritation Duo that started when I took out the Keeper last night.

I've washed the cup thoroughly, repeatedly, and it still stinks. Gross, I know, but nothing I do seems to work and I can't boil it because it'll melt. Frankly, I'm starting to give up on it (it smells and is possibly harboring yeast bacteria - or am I paranoid?) and contemplating just sucking it up getting a Diva. I've had the Keeper for 8 years now (it was a first period present) but have only been using it for the last three or so. Is it time to toss it?

Also, I just went and got plain Liberty Organic Probiotic Yogurt, dipped a tampon in it (I only have tampons lying around because the doctor told me last time that it'd be a good idea to use them so they could pull yeast out), put in the tampon, and tried to put in more yogurt with the applicator. How many times should I repeat this? I've heard it's the thing to do, does anyone have any other input? I want to try to stave this off as much as I can...