Ate a burger that was a little rare. worried i will get sick. have a little stomach ache next day. am i over thinking this? a little nauseous

Probably overthinkin: How long ago did you eat the burger? When did symptoms develop? What establishment was it, or did you make it yourself? Unless there is an FDA food warning / recall of beef in your area, most probably the "little rare" burger did not cause the problem. Burger joints are notorious for fixing fast, greasy, unhealthy foods- eat healthy in future. See a doctor about your symptom (nausea) if it worsens