Sometimes when taking a remedy, people experience a temporary worsening of symptoms. This is what we call an aggravation. The good news is it normally passes quickly, and if it doesn't, your homeopath will be able to help you decrease or eliminate an aggravation.
A confirmatory aggravation is one that happens right after taking the remedy and is considered a good indicator that the chosen remedy is correct. It shows us that the body is responding to the remedy by temporarily increasing symptoms and we can expect the disease will resolve as time goes on. There should be some sense of feeling better that arrives quickly, often just a general feeling of well being. If no positive changes occur, the remedy is not correct, or not the right potency, and it needs to be changed or adjusted.
This is much different than side effects that might be experienced when taking allopathic medications. There is no risk of harm with a homeopathic aggravation. It is not a side effect of medication, some of which can cause harm.
It is also not necessary to experience an aggravation in order for the remedy to work. Most homeopaths aim for symptom improvement with minimal or no aggravation. So if you don't feel worse, only better, that's great! In acute illnesses, I have observed that the more intense the symptoms, the less likely a person will experience aggravation.
My daughter came home from taking a test a while ago and went directly to her room, holding her head and in tears. She had a migraine which had started as she drove home. She felt like her eyes were being pressed out of her head, had significant dizziness, nausea, and felt like the skin on her head was too tight. I gave her Phosphorus and within 10 minutes she was able to relax. In a few hours the pain and other symptoms were almost completely resolved. She had no noticeable aggravation. In another instance, she had a sore throat which called for Sulphur. After taking a 30C, the pain in her throat increased a small amount, which I considered a confirmatory aggravation. It resolved within the hour and the throat pain began to improve until the next day (and one more dose), when it was gone completely. In the first case, the symptoms were intense enough that no aggravation was noted. In the second, the symptoms were less intense and an aggravation was evident.
If an aggravation does not go away on its own, get in touch with your homeopath, who should be able to help.