well..a folded up cup..i'm pretty sure no matter which fold you may be using, would still be bigger then a tampon. But with lube or something it could maybe not hurt so much. Do you have a lot of pain with sex as well?
Good news if you do end up trying the diva cup and it doesn't work out, they have a 1 year warranty (from the website, if you keep the receipts and what not, and don't cut off the stem, i believe.) so you could get your money back. All this info is on their website. (http://www.divacup.com)