Painful sex during pregnancy?

I need some help!
Sex is miserable during pregnancy.
This may be TMI, so sorry, but my doc was no help. As soon as I'm almost to... The go.... I get this sharp stabbing pain in my right lower quadrant of my abdomen! Brings me to tears.... And to more tears because it's ruined my... Go. 
I've been on top cause it's my fave, and that's when it happens.
Has this happened to anyone, or do you know what it may be? Helpp!!