Positive opk 15dpo

Hi ladies! I'm what I think is 15dpo, cycle day 38 today. I swore I saw a barely there line on a frer last Saturday and Sunday and have nothing since. Still no AF. I randomly took this opk today because I have tons of them and got this blazing positive that showed up immediately! I'm having bloodwork drawn tomorrow to tell me what's going on. I also had an hsg day 11 of my cycle. Can anyone shed some light on this? Has anyone had a weird cycle after an hsg? ​