Sc removal don, 2 weeks ago, bilateral arm pit areas. forgot to take the post-surgery antibiotics. cant fully extend either arm upward. is it too late?

Yes: No reason to start taking the antibiotics at this point. However, the antibiotics would have nothing to do with your inability to fully extend either arm. This is a mechanical problem likely as a result of not extending your arms for the past 2 weeks. See your surgeon and get a good examination of why your having a problem. Most likely, you will need good physical therapy and all will be ok.