Can a kidney infection cause diarrhea and nausea? i have lower back pain and those as well and worried it could be an infection since i just had a uti

Yes: severe kidney infections can results in blood stream bacterial infections which can become very dangerous if left untreated. Symptoms of systemic "blood stream infection" can included: fever, nausea, vomiting, diarrhea, dizziness. Please follow up with a doctor or schedule a consult to get lab testing if you prefer although in person evaluation is much preferred.