I hope you will just keep at it. Go out for half an hour while it's cool. Keep trying on the hills and you will get further after a while, but also build up your base riding on a flat area.
When I started I was happy going 3 miles, but pretty soon it was 5 miles and 10 miles and so on. The year I started I would sometimes get overheated on a flat ride less than 10 miles long. Drink a lot of water.
And stay connected here- you will get a lot of support.