Hmm, if you've only been playing for a month or two I'd say don't worry about it, it'll come back to you like riding a bike, but you've been back for a year and a half and can't put together a consistent level of tennis.
You have to be able to figure out what you're doing wrong. Are you not playing often enough, is it a physical fitness issue, or is a technical issue? If you're playing at least once a week and say you are in decent shape then it may be a technical issue and it'll help to work with a coach. If you're 46 and quit playing the first time at 16, that places the end of your junior tennis days in 1983 (they had Head Prestiges back then?) so you probably have classic strokes and might benefit from learning more modern strokes and tactics if you plan on competing.