Hi..
Welcome to HEALTHCARE MAGIC..
As per your complain white coating over the tongue seems to be due to
fungal infection known as Oral Thrush..
Post nasal drip can occur due to causes like
sinus infection, respiratory infection, acid reflux etc..
Twitching all over the body can be due to
Peripheral neuropathy or can be due to Vitamin B 12 deficiency..
Not necessarily HIV if it was negative after 6 weeks..
For Thrush you can be advised antifungal medication like Nystatin mouthwash, Clotrimazole lozenges and
Oral antifungal medication like Fluconazole, Itraconazole etc..
Taking plenty of Probiotics like Yogurt and garlic can help..
For twitching Vitamin B 12 and zinc supplements oral and injectable if found deficiency can be advised..
For post nasal drip first of all ruling out the cause and treatment can be done as per the cause..
For infection antibiotics, mucolytic agents like Ambroxol etc can be advised..
Hope this helps .
Regards .