Confused about DPO! Please HELP!!

Hi ladies! I'm new to this forum but have been using Glow since June. I'm 26 years old and my cycle is usually between 31-38 days. I'm currently on CD 36. (I haven't tested yet bc I'm scared of the possible disappointment plus I have no symptoms). My DH and I have been TTC baby #1 for 8 months with no luck. I've been using the clear blue digital OPK but I'm not sure it's accurate. I got a solid face on the 18th (with a flashing smiley face the two days before) which means I should have ovulated on the 19th right?? If so, I'm currently 18 DPO. However, I've gone as long as 23 DPO until AF comes. Is that normal??