I don't use the plural for paracetamol or any other drug name. I would use it if I were using the words "painkiller", "tablet" or "pill".
I have a headache. I'm going to take two paracetamol.
I have backache. I'm going to take two aspirin.
He has neckache. I suggested he take two ibuprofen.
She has stomachache. I think she should take two tablets.
I took two painkillers three hours ago so I shouldn't have any more yet.
In the UK, with the exception of Nurofen (which is ibuprofen but lots of people use the term for many painkillers as if it's the name of the drug rather than a brand name), we hardly ever use brand names in place of the name of the actual drug. In fact, with the exception of Nurofen, I couldn't tell you the brand name of any painkiller. The most common painkillers are just referred to as paracetamol, ibuprofen and aspirin.
In Australia, and throughout my medical career, I often used the plural - probably because patients do. I don't think it matters. It's more important to know that paracetamol is acetaminophen is Tylenol is Panadol, etc. It's also N-acetyl-para-aminophenol, but I had to look that up.