It is difficult to sex African bullfrogs when they are juveniles. You can tell that they are young by the vertebral stripe. Breeding males are often distinguished by yellow or orange blotches on and under the forelegs. You know that there are two species in the genus Pyxicephalus that are very common in the pet trade. According to my African frog field guides, it appears that you MIGHT have a dwarf bullfrog. The dwarf has a white spot in the tympanum, there is a faint interorbital bar (the line across the head connecting the two eyes and that the distance between the eye to the tympanum is about the same as the eye's diameter and the coloration is brownish-green. I could be wrong, just wait and see.