ttc but no luck

Jenna
So i have a daughter whos 7 and a son whos 3 from a previous relationship. Me and my new partner are trying for a baby ive been off my pill since september snd getyibg regular periords but nothing yet its getting me down i caught so easily with my other two i just dont understand why it not happening my partner had been tested before and has nothing wrong with his sperm so could it be me now even tho i have children? Im 30 and hes 34 and we so desperately want a baby to finish our family any advise