Need Help

I don't know when I ovulate! I used to have 35-40 day cycles and my doctor put me on metformin and I have been on it for about 3 months and now my cycles are 29-33. My doctor told me to have sex CD 12,13,14,15,16 to get pregnant. Well we did that and it didn't work. I just finished my period and am on CD 6. I plan on getting digital ovulation sticks but not sure when I should start them...never used them. When do I use them? FMU? We have been TTC for 11 months now and I am losing hope! Anyone who was successful using digital ovulation sticks (the smiley face ones) and what CD do I start? Anyone on metformin too?? Thanks!!