trying to conceive

Me n my boyfriend been trying to get pregnant for almost 3 months n no luck I get the nausea n sore breast along with peeing alot n eating alot n still not pregnant it's heart breaking I get all thos n then end up starting my period he had a son pass away from sids at 6 months old before we had got together his son would be 5 now so this is important to him as me but I already have 3 children with another person it's important to us both I really want another one but he deserve to have the chance to be a daddy to his own help :-/