Congratulations and keep up the good work.

I second the suggestion of using a trainer during the winter months. Using a trainer is boring, I'll admit but it pays off in huge ways in the spring. Do you have a local bike club? Do they offer "trainer tours" during the winter months?

Once it warms up and you are outside again on a regular basis ride and then ride some more. Try increasing your mileage by 10% each week and over the course of a few months you will find your endurance and speed increasing.

Do you have a bike computer? Does it have cadence? I would suggest you focus on your maintaining a steady cadence first, speed will follow. Find a zone, say 80-90, that you can ride comfortable in consistently and focus on spinning. As your strength and endurance builds try bumping your cadence up a little and again the speed will follow.

Keep up the great work!