Last winter, I went 6 weeks with just 3 or 4 sessions of 30-45 minutes on the trainer. Then in late January and February, there were a few warm days, so I did about 120 miles total in 5 different rides. I was slow, and worn out by the end of the rides.

Then in March, I got in 11 rides and 350 miles, with some 40 mile hilly rides. I was starting to get back up to speed. Now in April, I'm getting closer to my summer fitness. It's 650 miles for the year, with a 60 miler last weekend.

You just need more rides, and will be back in shape in a month or so.