You are right that it is difficult to put creans on large urticarial eruptions. If these lesions are red and itchy and resolve within hours but start again at different sites (part of body), it is most likely urticaria.
Triggers can be : physical (so do NOT scratch), cold/hot induced, stress
(makes it worse), occasionally menstruation-related, but more commonly idiopathic.
You need long-acting antohistamines like fexofenadine
180mg AM 90mg PM plus/minus cetirizine
10mg lunch time plus/minus hydroxyzine
25/50mg at night (ONLY). You may need the treatment for 6 weeks to 3 montsh depending on speed of resolution.