You're best going to a physiotherapist, but boxing will not 'help' strengthen your shoulder joints. As an example, I sprained the acromioclavicular joint in my shoulder about a month ago & I still have to wait at least another 2 weeks before I can do any light training (e.g. skipping, ground-work, speed-bag etc). It will probably at least another 3-4 weeks after that before I'm allowed to hit the bags again & even then I'll have to monitor myself. Definitely see a physiotherapist first about the issue