Many thanks for all the helpful comments and suggestions when I found my mouth was filling with blood a few weeks ago. I never felt ill with it but it happened about three times a day for about five days. After an endoscopy, the consultant said that the blood was probably due to a tear which had since healed. He found multiple polyps in the stomach which were caused by taking omneprazole. He told me to continue taking the omneprazole - and as a nurse said to me later, it's better to take omneprazole than to get a stomach ulcer. I asked if I should take yoghurt instead but he didn't seem to recognise this as an alternative.
Anyway, I'm very pleased that things have worked out this way. Thank you for your encouragement.