Oh, Georgie! My sincere sympathies. I really do know how frustrating the problems are. It obviously varies from individual to individual. FWIW, when faced with same problem, I cannot fast completely because certain drugs must be taken with food. I find that simple tinned salmon in a plain white bread sarnie works OK. Also simple, non-spicy rice (Tilda do an easy-to-use version).
Get better, my friend. Take care.