Originally Posted by eig
Her new meows are very loud. She had never meowed like this before in her entire life, I didn't even know she can be that loud. She drinks a lot and very frequently. This habit since developed into excessive meowing during the night.
1. The vet ran a couple urine test and blood tests and found nothing unusual. She had no clue why my cat would act like that out of the blue.
Did the vet test the T4 Thyroxine Thyroid hormone level in the blood tests? Depending on the lab used sometimes this is an add-on to the general blood panel, sometimes it's included in the Senior/geriatric/complete blood panel
Excessively loud meowing especially at night in all cats, not just the normally very vocal Siamese, can be a symptom of Hyperthyroidism.
Excessive and frequent water drinking & the resulting increased urine output can be a symptom of kidney issues.
If there is concurrent Hyperthyroidism and kidney issues the blood test may not reveal the kidney issues until the Thyroid level is under control.
If your vet has not already tested the T4 Thyroxine hormone level, I would suggest asking for that test to be done.
If it was done already & the result is in normal range but on the high side I would ask for a Free T4 test to be more accurate.
If it was tested already & is high out of normal range then your cat has HyperThyroidism & treatment options should be discussed with a vet.