There are 2 likely causes for what you have described. The first is that you have experienced a viral infection. This has caused postnasal drainage and the fatigue. At this time of the year, vial infections are fairly common. It can take weeks for this to go away.
The second cause could be a sinus infection. Amoxicillin does not take care of lots of types of bacterial sinus infections. There are lots of other antibiotics that can be tried to treat this, if it is a sinus infection. A sinus CT would tell if you have a sinus infection.
It is not clear if the anxiety issue has any bearing on what you are describing.
hi,my daughter has coughing for over 5 months,drs treated her for asthma,and cold for mnths got so bad she was throwing up plegm in large amounts,finally took her to lebonheur childrens hospital where she stayed 2 weeks ,she had severe sinus disease which had to have surgery,severe acid reflux(gerd)which contributed to her coughing and candid esophagitis,her esophagus was infected from the stomach acids,that alone will give someone a continuous cough,hope that helps some
I had a similar problem a few months ago. I did some reading and found that my symptoms were similar to those found in cushings disease. I evaluated what had changed in my diet and finally found that I had been eating yogurt 3 times a day which contained active yeast which caused the symptoms. As soon as I stopped eating the yogurt, my tongue returned to normal along with the other symptoms. Just some food for thought.