Well I'll wish you luck because I can totally relate. I bought my bike at the beginning of April and have been riding 4-5 times a week since then. I am 46 and was quite out of shape but I am loving it and boy am I ever seeing some improvement - so you can do it and it *will* get easier! I could barely ride 6 miles without a rest break at first but now I can 30+ miles with ease and I'm slowly increasing that every weekend.
I have a mountain bike too for similar reasons but I have semi slicks because I ride mainly on the road and I really found that is helping. I think I want a road bike deep down though...I have found having a bike computer and recording info about every ride on bikejournal.com has helped me see my growth and improvement.
So good luck, and keep at it!! (This site - TE - has tons of info and support..)
Barb