I could find no reports to suggest (what is called) cross-reactivity between Bactrim and
Cefdinir. That
does, however, not rule out this possibility. You were wise to stop taking the drug and contact your physician. You ask is this an allergic reaction or a symptom. The sensations and numbness you describe would fall under the heading of symptoms. The symptoms could be caused by an adverse reaction to the medication that could be either allergic or non-allergic with inflammation.