Ovulation

Mrs • I`m 33 w/3 daughters & a 1 son.. I have been w/my husband 15 yrs, but only been married 5 yrs
Had procedure done July 1. Haven't had af since I left thehospital, which was July 2. How will I know when I'm ovulating?? I don't want to get pregnant to fast & end having another ectopic pregnancy.. Or where can I buy ovulation test from??