With only a small number of fish, it is also possible you have all males or all females. When I want a fairly good chance of getting a pair, I buy 6 or more juveniles. That gives me over a 95% chance of getting at least one pair of fish out of the 6 juveniles. If you bump up to 8 fish, the chances become very high, over 98% if I remember right. Time will tell but it is still too early to panic, as helterskelter said.