ovulation test HELP!

Kay
Need advice! I'm on CD 15 of a 28 day cycle. I stay pretty regular. Actually took my very first O test today on cd 15 and got a faint line and a negative on the digital :( shouldn't I be in my peak fertile time by now?! I already have one son so I think I can conceive again but now I'm feeling super confused.
TMI but No EWCM as of yet either /: just dry or slightly watery if anything! 
Anyone have any advice?!