Hello Everyone, I have an update from my lovely vet
Dexter either has an infection or a severe stomach irritation, so he's had an injection of antibiotics, special chicken and rice food for the next 5 days (it would hae cost more for me to buy the chicken and cook it lol), a probiotic and a course of antibiotics, and she clipped his nails for free. Small favours!
And now he's rolling around the floor with his toys as if to say "I don't know why you were so worried mummy", cheeky thing.
Thank you for your support and advice.