Very thick penis is being a problem in the bedroom.

So basically my gf and I have been having problems with the size of my penis when trying to have intercourse. There are times we are able to have sex without it being a problem but seemingly randomly there will be times when sex leaves her very sore and this normally is followed by a week long break from bedroom activity besides oral so that she can recover. The cause of this I feel to be the thickness of my penis, in length it is a pretty standard 7 inches but the girth is too thick for her fingers to touch when she puts her hand round it and if I am receiving oral she has to open her mouth as wide as she can to fit it inside. We have tried two types of lube (KY jelly, and Ann Summers) and have tried with and without a condom as she is on birth control. So what I am asking is do you have any advice on how to work things so she isn't caused pain when we have sex. Any advice or knowledge with this subject would be greatly appreciated.

TL:DR I have a penis with a lot of girth, gf is in pain from it, how do we do things so she doesn't hurt? We have tried loads of foreplay, condom and no condom, and two different types of lube.