Oh WOW!!!! CONGRATS!!
No question that's a BFP

Getting a BFP on 10 dpo is really common with the great tests they have these days. My little sister got a BFP in December at 10 dpo at 11 pm w/out FMU

In the morning she used FMU as it was equally as dark as yours (but she used 1st response).
How long are your cycles normally? It would appear you have a healthy lutal phase because you did achieve pg (

). If you normally have a cycle that's around 28 days I'd go w/ O on CD#15. If you tend to have really short cy's around 22 days I'd go with O on or around cd#8.
Either way, give your Dr. a call and let him or her know you are not clear about your dates, they will likely do an internal U/S. An early U/S is really quite accurate at pegging down dates
Have a H&H 8 (ish) months