It makes me mad that your BF isn't being supportive. He should know how super hard this all is and that you need comforting not more garbage about exercising. If you felt well enough then you would try it. Doesn't he get that you hurt and feel unwell???
I personally believe that one shouldn't exercise if they're sick or feeling pretty unwell. I believe that it negatively affects the immune system instead of helping it out. I say if ever you feel great, go for a walk with your doggie, but I don't think you shouldn be joining a gym anytime soon.