What Causes Vaginal Discomfort And Pain During Insertion Of Tampon?

I am on my period but it hurts when i put a tampon in, could this mean that i may be pregnant? I had sex about 1 month ago, and also when i had sex it hurt. When i had sex last month, it was my first time (with the same guy, college boyfriend) in about 4 months. I am 18 years old and he is 19. Also, i get side cramps and at times chest pain in my breast. Not when i use the tampon. But it does hurt when i enter it in.