I am sorry your baby is having trouble.He sounds wonderful!
Jaundice would be obvious because his gums and eye whites would appear yellow.
Blood in his saliva could be due to a dental issue, stomach ulcer, biting his tongue, IBS or swallowing a sharp item.
Check under tongue, roof, cheek pouches and between lips and teeth for any abnormalities.
Weight loss is usually related to hyperthyroid. The cats eats great but the excess thyroid hormone burns up all the calories.
The problem is that this disorder can lead to your baby developing diabetes, high blood pressure and other ailments.
We do have excellent meds for this but is is necessary to do a T4 thyroid blood test.Any other thyroid test can be inaccurate.
It can also be related to renal issues especially if there is excess shedding because the hair becomes very dry.
Stress weakens the immune system and can lead to illness.Dental disease also depresses immunity and sends bacteria into the organs.
Some dental issues can only be diagnosed by radiograph.
For more information on Feline Resorptive lesions, please visit the following links:
Vomiting can be caused by eating dry food or a stomach issue and can weight loss.
Your baby does need a vet exam to ascertain the cause of the blood in his saliva and his weight loss.
In the meantime feed him light soft foods like canned or baby food (no onion powder)
PLease let me know the outcome of his exam.
I hope all will be well.
Warmest best wishes,'