My poor little guy 
Adopted cat from rescue last year. He is 8years old, siamese. Had a hard life, bullied by other pets in house pre adoption. He is lovely. So affectionate, loving and gentle.
I lost my dad recently so went to mum's for Christmas as did not want her on her own. It was short notice but we found a well recommended local cattery and the woman has four siamese of her own so knows the breed. It was for ten days.
When he came back he was very stressed. Bad tummy, lost voice, lost some weight. He seems more settled now but he is still having tummy issues (have read siamese have delicate constitutions when upset). He has had diarrhoea and vomiting, sometimes up to 3 times a day. We feed him Waitrose own wet food (high meat %) and Wellbeloved dry food as is his normal diet. The vet has tested for diabetes, kidneys, liver - came back clear. He has been wormed and had a course of antibiotics. We tried vet food for delicate stomach. He often eats grass which induces vomiting and there is usually grass in his poo.
ATM on vet advice we are feeding him chicken and white fish only which seems to calm his tum down but it is £££££ and really isn't the root of the problem.
He is otherwise happy, hungry and active. No other signs of stress or illness. So WTF, cat?