Can't wear tampons anymore..

My last two periods have been ridiculously light and spotty when normally I have a steady flow that lasts 3-5 days. Now, I'll bleed enough to wear a tampon for about 3 hours and then my flow will dry up and then I just spot. I use a pantyliner but most of the time the blood doesn't even go on it. Has anyone else had this problem? I'm not on any birth control or any medication and not stressed out.