He's going to check your hormones (progesterone and estrogen) to make sure they are at normal levels. After you ovulate your progesterone should be higher, that's why he's having you come back on day 23.
Honestly, it's better to just track your temperature everyday starting on your period. This can tell you for sure if you are ovulating and if your luteal phase is an appropriate length. You take your temp every morning before getting out of bed, and at the same time every morning. Once you ovulate your temp will go up and stay up until you start your period. if you are pregnant it will stay up. My morning temps are usually around 96.8 before ovulation, and 97.6 after. If they go up and stay up for at least 10 days, then your cycle is just fine.