My creatinine blood level was 0.55 mg/dl in dec and in feb was 1.11 mg/dl. is this cause for concern?

Could be: There are minor variations in results done at different times, however, the disparity you described is too large to be ignored. Ask you doctor to repeat the test and look at your eGFR. If the eGFR is less than 90 it would be useful to see a nephrologist.

See primary: The creatinine change could have been the hydration status or if taking NSAIDs such as ibuprofen Or naprosyn etc.Some meds such as ACE inhibitors can cause a change.These test must be considered in the clinical context.I would look at the more GFR and make sure no protein in the urine.Most workup can handled by primary care til GFR below 30 per Most nephrologist unless significant protein in urine

Creatinine: The creatinine level is still within normal limits although in the upper limits. I advise checking it again in a month to assure that it's not climbing. Also obtaining a serum BUN and a urinalysis would be a good idea.