Sir When I Fuck A Girl For Two Times In

sir when i fuck a girl for two times in one hour and then third time after one or two hours again then my penis is not standing easily and not hard mostly i failed third thats mostly in rain or cold season but in hot day or season does not same position in hot day easily 4 time i will do fuck in three hours my question is that why some time spacially in cold weather i failed for third time my age is 40 years what the problem with me?