Does the child have a fever very often these days?

The weather is really getting hot these days. My child has been sick frequently, and the lines at the pediatric clinic are so long that the morning just passes by. Maybe because the child lacks stamina, they seem to have a fever often. Whenever we go to the hospital, they always say the tonsils are swollen. After recovering from a cold, the fever comes back after a few days, and it repeats, which is exhausting and worrying. I wonder if I need to boost their immunity; it's really difficult. The child also often loses teeth at kindergarten, and they can't eat much to gain weight, so they lose weight again, which is upsetting. Should I give herbal medicine or nutritional supplements?