If you've seen three or four, and they were all nymphs, then there is a colony close by. Don't call pest control quite yet, though; put down some glue traps, and see what you catch. FWIW, this is not a German or Brown-banded cockroach nymph, and those are probably the worst for infesting houses. I don't recognize this species, but it's a nymph, and I'm not as familiar with TX roaches as I am with those farther north. It may be that it's an outdoor species that has just found a point of ingress and is looking for a place to spend winter. In that case, you don't need to spray your home; you just need to find the entry point and seal it off. Native cockroaches belong outside and they know that, and they actually perform useful functions as detritivores, so they shouldn't be killed for no reason.