Help with confusing ovulation dates!

Hello!  31 y.o. TTC # 1 with DH (33).  I just got off BC pill at the end of August.  AF September 2-8.  EWCM and cramping on cd 10 (sept. 11).  Very frisky that day and the day after.  BD numerous times that week as we were on vacation in the UK.  Once we got back home, I started opk and all were negative until I felt nauseous all day today and got a positive on cd 23 (today)  What is going on?  I know is nearly impossible to ovulate twice in a month.  I'm a registered nurse and know about the process, but all this TTC stuff can be intimidating.   Any ideas?  Thanks in advance ladies!