I had to divide my response into THREE SEPARATE PAGES because the length did not allow it to be uploaded...
PART ONE:
My sincerest sympathy and empathy with what you've undergone!
I totally concur that the hospital has to be held accountable. You've been seriously and adversely affected by whatever action or lack of action THEY imposed on you.
Must be so painful to try to even sip a non-irritating liquid, let alone try to place a bit of nourishment into your mouth. Totally unacceptable that the hospital washes its hands off the consequences of your having been in THEIR dubious "care"!!! So their stance is that it is YOUR tough luck, leaving you to "deal with it"??? Immoral, unethical, irresponsible, and definitely litigious.
Does your country have free legal counsel for eligible citizens? The term here for free legal representation is "pro bono" --- the lawyer gets no monetary compensation UNLESS he/she WINS THE CASE. You would owe NOTHING if he/she loses the case. Each law firm has parameters which you must clearly understand before signing on for legal representation...

See what of the following (that we have rights to) you can do for starting your quest:
• Request your medical records, ALL that relate to your specific hospital stay. Specify DATES, and state "ALL records, including bodily fluid tests, radiological and any other testing, related to RSV, the hospital stay for --???-- (give DATES both beginning and date of discharge)
•Request that doctors' summaries of each and every in-office and in-hospital interaction with you be included.
You might have to pay a per-page fee. (At the very least, you have the right to request access to your records, and provide you a space in which you can sit and search through your records; perhaps you can use cell phone to take snap-shots?). In the event of lawsuit, your law firm would be responsible to requesting, obtaining, AND paying for copies of the records. THEY contact the appropriate department (here called Medical Records), and THEY get the bill for copies.
•Seek medical help for whatever field of medicine in your country would deal with mouth conditions. Here, it's ORAL SURGERY. You ABSOLUTELY need to have that highly suspicious growth examined, and tested (as with biopsy), and determination made as to specific medications deemed necessary to be prescribed (as appropriate). In MY HUMBLE OPINION, an over the counter mouth rinse/ointment is inadequate and inappropriate. Might soothe/numb pain at best. While I am not a doctor, I did hold certification as a medical assistant way back in my late teen/early twenties (am now 77!), and I did have training/education in anatomy, physiology, blood history and analysis, cerebrospinal fluid testing, radiology, cardiology, and so much more learned while working with a major medical/teaching complex in NYC. All of that has armed me throughout my life when dealing with medical issues involving our children, my husband, my mother and sole sibling (a brother), AND my own laborious medical journey. So I encourage you to PLEASE ADVOCATE FOR YOURSELF.

SEE PART TWO...