My bub is 16 weeks now and I am up to my 4 doub...

My bub is 16 weeks now and I am up to my 4 double course of antibiotics for Mastitis - YUK!!! It just keeps coming back! BB has now got thursh in his mouth. The doctor has given me Nilstat to be used 4 times a day. She didn't say if that was before or after a feed?? She hasn't treated me for thrush and I am now experienceing sharp pain of the nipple, different feeling to Mastitis. It must have thrush. I have also been to the chemist regarding the daktrin gel, but the packet states from 6 months. Has anybody used this for younger bubs?? Any advise would be great, I am just miserable and am considering weaning to a bottle.