Yeah, been there myself... just a shade over a year ago.
Started riding April of last year after a 20 year hiatus.
I could go around the block with stopping 3 times.
There's a 1/3 mile false flat... I was in a pretty low gear and could barely get over about 6 or 7 miles an hour. Well, I just kept at it and the miles -and my gear ratios- started increasing pretty quickly. Now I do 20-25 mile rides without much thought.
I also might point out that a year ago I weighed 225lbs -a lot for my 5'10" frame- and now I'm holding pretty steady at the mid-190s looking to drop at least another 10.
You've taken a good first step -starting- now keep on keeping on.
You'll find a tremendous amount of support here.