Can’t use tampons, help!!

Okay, so I use to always use tampons when I was on my period. I never used pads because they always were uncomfortable for me to use. Anyways, so I have always used tampons and never had any issues with them until I got the Depo shot a few months back. And I’m not saying that the depo shot has anything to do with it, that’s just when I started not being able to use tampons without any discomfort. Now, when I use them, they hurt so bad, like when I’m walking, sitting, doing anything pretty much. And it’s not like I’m not inserting it correctly, I’m doing it the same way I used to do it when I was able to use them without discomfort. And I’ve tried SEVERAL times, to take the one that’s hurting out, and put a new one in just to see if it was how I was putting it in, but every time it’s still the same. Also, the depo kinda F’ed with my period, bc now it comes randomly, it’ll come for like a day, go away for like 3 days, and then come back, it’s all unexpected. Anyways, so ladies any idea as to why this is happening or what I’m doing wrong or anything?