Husband will not tell his whereabouts. Should i be worried?

He ures me that he is not seeing other women. he is just out there drinking with his office friends. if i try to call him, he always has this excuse that he was not able to notice my calls because it's on silent mode and he is really occupied with his friends conversation. he also gets home at wee hours in the morning. i believe him that he is not having an affair but this behavior is really starting to piss me off. what should i do? am i over reacting?