Should i use aqueous cream on an allergic skin rash? why do they call it aqueous cream?

Yes if it's eczema: Use creams & ointments on eczema. Lotions & gels contain more alcohol. They soothe & cool the skin by evaporation but evaporation causes dryness. That's the last thing you want in eczema. Creams & ointments trap moisture in the skin - better for eczema. This is less important for contact dermatitis and not at all for hives. Aqueous means ingredients are dissolved in water.