I'm dealing with a similar issue (not the weight gain part, but the injury part). In the past few weeks, I've been taking these daily epic 2-3 hour walks/hikes, which is really exciting for me because:
1) I've been struggling with debilitating fatigue in the past months, and I finally have the energy to move around now.
2) Walking generally improves my mood and makes me feel good about myself physically.
3) It's blazing hot now, and the 90-100 temps don't bother me one bit!
However, during one of my walks, I seem to have developed some kind of weird pain near my knee that I'm assuming is tendonitis. Following my usual bad advice to just 'push through it', I think I made it much worse, which ended up with me not being able to walk much for about 1.5 weeks.
I SHOULD HAVE waited longer, given my body more time to heal, but since I wasn't feeling pain, I pushed myself too much with a 2 hour hike yesterday. That damn pain came back, and now I'm probably looking at a MUCH longer recovery time, which is torturous, I just want to get out there and move around!
So, I feel your pain, and honestly, I don't think that overexerting yourself right now will do you any good. In fact, you'll likely extend your recovery time, if anything. Our bodies have some amazing healing abilities, but only if we give them what they need. If your body is focused on intense excercises, it won't have the manpower to ALSO focus on healing.
When you are 100% healed, I'm sure it will take you no time to get back to where you were before the injury, so I wouldn't stress about it now.
Keep in mind I'm not a physical therapist, so I could be totally wrong - this is just my opinion based on my experiences.