Why does it hurt after sex?

so me and my boyfriend have both been given each other yeast infections for a while now and we have both had the pill for it yet i think ive had it again. everytime me and my boyfriend have sex after it burns and we get belly pains and i get a dull ache blow inside. but apart from when we have sex and just after we are both fine and no other symptoms. i herd that yeast infections can travel up inside you. any ideas?