Trying to conceive

Me and my fiancè have been trying to conceive for almost 6 months now , he ejaculate in me 1 or 2 times a day , this would be baby #1 for us ! But nothing is happening , the most I get is pains in my stomach constantly and heart burn but then I always start my period late and every pregnancy test comes out negative, advice on what to do to help speed up the process of conceiving and what could be causing those ?