Echoing the responses from others to first confirm there are no health issues that would preclude you from pushing yourself harder. Then, increase your miles gradually. A couple of miles won't even warm you up.
I see you're from CT. Yeah, hard to avoid hills. Maybe consider driving your bike to one of the bike paths. Check out the Farmington Canal Heritage Trail. I've only cycled portions up in the Farmington/Collinsville area to get to one of my road loops but I think you can pick it up in Cheshire, which I think would be closest to you. If you can get your bike to a parking area, you could ride your bike increasingly long distances on the bike path. The Airline Trail is another nice bike path although the nearest point you you (assuming, per your profile, you're in Wolcott) is East Hampton. As you increase your distances on the bike paths, you should find you'll get stronger and can introduce some hills to your rides. But, it does take time to build up endurance. Best of luck.