I've had diarrhea, fatigue, tense muscles and dizziness for three days. should i see a doctor or is it likely a bug that will resolve?

Yes-Maybe dehydrated: Treatment depends on problem (have soft or watery stool?), circumstances under which diarrhea developed (altered activity, food intolerances, stressful times, ischemic gut, inflammatory colitis, antibiotic use, exposure risks, rectal dysfunction), severity (stool volume, dehydration, how much blood, night-time awakening, weight loss), duration (acute vs. recurrent? See UR doc for worrisome signs.