It's possible that one of the screws or nails you used to fix the drywall pierced a wire. If you cut the circuit breaker, turn off all the switches, and connect an ohmmeter between the hot and neutral, you should get infinite resitance. Then turn the lights on one buy one, and every time you trip a switch, the ohmmeter should show just about zero ohms. When you find one that doesn't make the meter move, there's a fault wither in that switch, that fixture, or in the wiring between that fixture and the previous one. That may tell you where you need to tear out drywall to find the problem.
When you're working in the main panel, beware that you are working in an extremely hazardous area. If you don't have training and proper safety equipment, it's probably best to find someone that does. Remember that the panel is always full of 240V and far more than enough amps to kill you if you make a mistake.