Baby is turning into a cryer !

My baby girl is 3 months and before she was a great baby never cried at all but for about the past week or two she has been fussy at night. I dont know if it's because shes not napping as long as before and is just tired by the end of the day? but she just starts screaming/crying. I check if she needs a diaper change and if shes hungry and all seems okay idk if she just wants attention? But even if I'm cuddling her like before to put her down for a nap she cries. I just dont know what to do I feel like a bad mother when she just cries! Can she be teething ? Anyone else ? Advise ?