Can anyone help please

I have two kids now my daughter just turned three my son I had for my sister cause she couldn't have kids if her own my hubby abd I have been trying for seven months now we want another baby so bad but it's just not happing I'm to the point I want to just give up :/. My hubby now is not my daughters real dad but he might as well be he's been with her since she was born. He really wants of his own and I really miss the baby stages :( we have tried everything from over the counter vitimes  to well just everything