Hi Brandon,
At the risk of bringing up and old cliche, the honest fact is that penis size is a small part of one's sex life. No pun intended, seriously.
Here's a video we did on the topic...
Does Penis Size Really Matter?
To answer your question directly, getting in better health and losing weight should greatly improve your sex life, from ability to attract women to vitality, endurance, and overall sex drive.
But what really, really matters in the bedroom is knowing what you're doing - case in point, most women think the only way to stimulate a woman is with your penis - which is blatantly incorrect.
There are plenty of threads in these Forums on that very topic - just a suggestion for you to check out. Read up on "female orgasm", it'll be very worth your time.
Here are
some resources to get you started - a search for "female orgasm" on AskDanAndJennifer.com.
Including especially the following...
Let us know how it goes!