You have two real options here, considering your visa could run out any day.
You can 1. return to the US apply for a fiancée visa, return and get married in the UK within 6 months and when you are married apply for your FLR which will let you work
Or 2. You and your gf can return to the US together, get married, apply for your spousal visa and return as a spouse directly which allows you to work from the start.