Hello Lady Jen, Severe left flank pain is likely always due to UTI (particularly kidney infection or pyelonephritis) and if the ER called to confirm infection with Staphlococcus haemolyticus then you need to be provided with an appropriate course of antibiotics. Note: Staphylococcus haemolyticus is a member of the coagulase-negative staphylococci. It is part of the skin flora of humans, and its largest populations are usually found at the axillae, perineum, and inguinal areas. It also a remarkable opportunistic baterial pathogen that is well-known for its highly antibiotic-resistant phenotype. Ones they are found in some particular organ system such as the kidneys they can result to a serious infection which might require hospitalization before treatment is initialized. My recommendation is that urinalysis + culture+sensitivity test, blood culture+ sensitivity should be done. You should be admitted with IV treatment for a few days. Treatment should include an indicated (from culture) antibiotics, analgesic pain killer, antispasmodic and IV fluids. Of course the final decision will depend on your treating physician since he still have to evaluate your general state and decide on whether you need to be admitted or treated ambulatory. Hope this helps and wish you the best.