Help! Not sure....

My hubby and I just finished having sex and he told me his "head" was hitting something kinda hard inside me? This is my second pregnancy and I never noticed this with my ex (given, his penis was smaller) but still it caught me off guard lol what could it be? Should I be worried? Its just something I haven't experienced so I'm just wanting to make sure. I'm 22 weeks pregnant. TIA for any help!