What Causes Itching And Feeling Of Lump Inside Vagina After Using Tampons?

I just started to use tampons during this period. My vagina started to itch a little so I scratched it, come to find out I felt this little sized lump on the inside of my vagina. This isn't the first time I found one. I used to get them when I was about 14-15 and that wad before I was sexually active so I figured it wasn't an STD. Now I've had sex 3 times with the same person and this is the first time I've gotten a lump in years. I am now 18. I jus find it ironic that once I use a tampon this happens.. any ideas?