Need help finding a story

I'm looking for a story about a guy who works as a paramedic and some old man sends him back in to the past. Makes lots of money from the stock market, saves his parents marriage, saves his sister from getting in to her boyfriends car which goes over a bridge and kills her in the previous life. He keeps his mouth shut about his affairs and gets to have a lot of girls including his mothers friend with whom he has an affair and later sets her with another guy. I think that's how i remember the story, let me know if anyone know the author or the story. Thanks.