Vaginal pain...

Lacey • Mommy to an Angel 1.14.16; wife 9.24.16; rainbow baby 4.4.17 && Baby #3 Due 4.28.20
In January I gave birth to my son, and had a 2nd stage tear. I've obviously since healed, but now I'm having pain and I don't know why. When my fiancé and I have sex in the missionary position, it's so painful, but if we have sex with me on top or him from behind, it doesn't hurt at all. I don't get it. Anyone else experience this?