Hi, I'd like to help you with your question.
It sounds like there are some issues going on here for your husband. Since you have tried to talk with him and you are interested in being with him sexually, then the conclusion is that this problem originates with him.
It is good that he has already gone for a full physical to rule out any problems. It is noteworthy that he was prescribed Viagra and chose not to take it. That shows he is communicating his feelings with this gesture.
It could be that your weight gain is affecting him. But keep in mind that many couples who are overweight enjoy an active sex life. So again, this is an issue he has and does not necessarily reflect on your attractiveness.
I highly recommend you both attend therapy to help you find answers. You need to have a neutral person help determine what your husband is feeling and what is preventing him from expressing himself sexually with you. You can find a therapist either by talking with your doctor for a referral, or if you attend church, your pastor is a good source for information or even counseling. You can also find a therapist on line at http://www.findatherapist.com/.
Also, until this problem is resolved, the two of you may want to find other ways to express your love for each other. Cuddling, leaving loving notes for each other, small gifts, hugs, and simple touching can all make you feel closer and help to rekindle your sexual feelings for each other.
This book may also help. It is called Rekindling Desire: A Step by Step Program to Help Low-Sex and No-Sex Marriages by Barry W. McCarthy and Emily J. McCarthy. You can find it on Amazon.com or your local library may have a copy.
I hope this has helped you,