Lump in breast

Hey all, I am 35yrs old and about 5weeks ago I found a lump in my breast (upper outer area of breast). I contacted my GP who asked about my menstural cycle, and then said if the lump was there after my period I should call back. So now period has passed and I still have this lump... however it's difficult to find when I haven't had a bra on for a while (sometimes I can't find it u til I've had a bra on a good few hours), I have D cup breasts so on the slightly bigger side. Has anyone else experienced something like this? I have called my GP this morning and I'm waiting for a call back. 
thanks for reading :)