It sounds like your baby is possibly laying funny on a nerve. When ive had things like that happen I'm pregnant with baby number six I tried pushing not to hard on baby toget them to move a bit. Sometimes it helped. Also heating pad not to hot for to long though.hope u feel better
If you're having swelling in that leg also it could be something serious like a blood clot. If not it's probably a pinched nerve and should get better over time. Call your doctor if you have swelling and pain in one leg only.