I would worry too much as at 14 weeks, there's still plenty of room for baby to hide in there. It could be behind your pubic bone, but I remember one time I tried to find it down low and I couldn't.. so I got really worried and thought "I'll just try a bit higher..." so I tried just a tiny bit below my belly button and there it was, clear as day, which suprised me as I thought it would still be really low at that point.
Try a bit higher, drink a cold drink, eat something very sugary and try again. But to be honest, if you still don't hear anything, I wouldn't go into panic mode. Just stay calm and double check with your midwife.