I had a long lay off due to having some pretty serious operations (full anaesthetic jobbies) on my nose in December. I started gently in February, mixing road and turbo + a weekly one hour session of light weights and rowing (machine) in the gym; by last week I had built up to a 90 mile week after these first two months. All very frustrating but I am now feeling reasonably good after feeling lousy at first.
I have another small op to improve things cosmetically in the next 6 weeks (just day surgery this time), which will keep me off the bike for a further month. I'm hoping that it will be a quicker process getting back and with luck the weather will be on my side this time.
My advise is to increase your effort incrementally, keep a record of what you are doing - I do weight, distance, time and average heart rate. Don't try to push yourself to much too soon.
Good luck.