Aggravations such as this are common when candida treatment is begun, especially when taking anything new like Florastor. Congestive headaches tell you that big changes are occuring in the digestive system, but it should also be a caution to you to back off a little.
I always get patients to back off when they aggravate. Focus on your diet and bring the same treatment back into place but in a significantly lower dosage. Head complaints are common when you work on the bowel, a warm shower can often bring relief and so can bowel cleansing. So can essential oils and a good massage of the upper back, neck and shoulders. There are many ways you can get relief. Don't freak, aggravations are most always manageable, but the trick is not to aggravate too badly.