I totally understand your concerns regarding the sweating issue.
The following points should be taken into consideration:
1- Sweating is one of the symptoms of infection, and according to the history you provided, you are suffering from a
sinus infection. So sweating is not an unusal symptom in your case. Thirst is a feeling from your nervous system that indicates
dehydration. If you are excessively sweating, you are losing water, you become dehydrated and hence you feel thirsty. One other clue to know if you are dehydrated is your urine output and urine color. If you notice that your urine is darker than usual and that you are giving less urine then this is also a sign of dehydration. In such case it is highly recommended to keep your water intake because dehydration can lead to severe electrolyte imbalances with a lot of complications and can lead to
kidney injury. Your body needs water, so keep drinking. When the infection is over then you will stop losing water by sweating and your thirst will go away.
2- I just want to make sure that this a sinus infection. The fact that you were switched from an antibiotic to another is unusual, especially from a third generation
cephalosporin such as cefdiner to a less broad spectrum antibiotic which is
amoxicillin only. I prefer a revevaluation of your infection, make sure that the lungs are clear, rule out all the possible differentials associated with night sweating and loss of weight.
Best Regards