Suggest Treatment For Infertility

my girlfriend and i have been trying to have a child for 4 months now and she just got her period again today. she had a child with another man when she was 17 years old WHILE he was wearing a condom and she supposally also took PLAN-B after the condom broke which maybe a lie, please help, we have sex everyday and i ejuclate in her everytime.. the sex is amazing she cums at least 10 times everytime we have sex and mulitipal orgasims, please help...