I had appendicitis 2 weeks ago & now I have stomach virus. Constant water diarrhea, what should I do to stop it? Imodium (loperamide)?

Concerned. Is there any chance you were put on antibiotics post surgery? You almost certainly had antibiotics at time of operation and your history is worrisome for c difficile diarrhea a cause of severe loose stools as you describe. Regardless, you simply must be seen and diagnosed for your own safety and health. Please do not delay.
Call doctor ASAP. Laura - you may have a secondary infection called c. Diff, which commonly presents as your describing. Call your doctor immediately or just go straight to their office. This needs to be evaluated right away.