While I know that women do not climax everytime,my girlfriend has never had orgasam during intercourse without manual stimulation at the same time. Is it me? How do I get to her G-spot?[She is overweight and doggy style is very difficult if not impossible.]

You're going to have to ask her and some experimenting. While the G Spot is usually in about the same place in all women, near the bladder all women are different so you'll have to figure out where hers is and how she likes it touched.

She sounds normal--very few women will have an orgasm from intercourse alone WITHOUT manual stimulation. She's in the majority here.