hello and welcome to Health care magic,
I am Dr Sriram Nathan and I shall try to help you out with your problem
The white line around tonsils and red spots on the mouth since is of a short duration can be due to many causes most of which are begnign and harmless so you do not have anything to worry about.
You may start a course of antibiotic like amox-clav along with an anti reflux medication
. Your doctor will know about these.
Take only non spicy, non oily and warm food and fluids
Look out for any dentures or teeth which is potruded and may be impinging on the said area
Take a course of multivitamin
like zincovit in consultation with your doctor
For your post nasal drip
you may need to take an ENT consulation to rule out sinusitis
and also do steam inhalation
If you do not get better in a week or so then you must consult an ENT doctor who may advice further course of action which may include biopsy
take care and do not worry
Dr Sriram Nathan