Pain & Pressure With Tampon Usage, Why?

I am 29 and used to use tampons 100% of the time for years, I'd say age 13 to 22. I've been on the pill for about 14 years and in the past 7 years I've skipped periods by continuously taking active pills... I have a period about once every 3 months. In the last few years I have found it incredibly difficult to use tampons to the point that I rarely can tolerate it. I've tried different brands and the only ones I can sometimes use are Playtex Gentle Glide Slender Lites & Slender Regulars... both of which still cause some discomfort. I often feel as if the tampon is causing my cervix to clench down, there is an annoying pressure and having a tampon in often causes cramping when I wouldn't have any using a pad. I never had an issue using tampons of any sort prior to the last few years and I loath pads greatly. I've had no change in sexual function, no pain with intercourse or change in partner... I'd really just like to understand why my body doesn't tolerate tampons anymore.