Short cycles and TTC

I have a very short cycle (16-17 days) since it normalized after being on birth control. The past three cycles have been 16-17 days. I have tracked my bbt and used opks since March and have clearly had a spike in temperature that coincides with when the opk says I'm at high and peak fertility. Has any one had experience with this? Tips or tricks? I have a doctors appointment for Friday to figure out what's causing the short cycles but figured I would ask here since I am pretty sure I am ovulating today or tomorrow and have been high on the opk for four days.