If I took one imodium (loperamide) plus an hour ago can I take promethazine?

Best not to. Imodium (loperamide) & Promethazine have an additive effect such that you risk severe constipation/paralytic ileus. Give the Imodium (loperamide) time to work. Continue to replace fluids—water or beverage with electrolytes (sodium, potassium). If no improvement or if worse, see your doc for evaluation & treatment.