Had flu and uti .taking antibiotic and lots of water. can this decrease my hemoglobin from 11.2 to 10.3 i had heavy period between the two tests?

Heavy period: Most likely your heavy period is the explanation of your anemia-rather than your antibiotics. Yes, sometimes, people can have drug reaction that causes destruction of the red blood cell etc. However, iron deficiency anemia as the result of your heavy period is most likely the reason of your anemia. I encourage you to go to see your primary doctor and get some evaluation on the anemia.