Mimi,
Sorry for the delay however I just read your post. I am not sure if you found the source of your gnats, but when Norm and I lived in FL we had a similar problem and I was able to find the source was the master bath due to the large master tub with a glass tile window that they were attracted due to the hot sun where most of them would just die from the heat. The rest would wander around the house. A plumber gave us an easy solution, pour lemon juice down all our drains for several days and it would resolve the issue.
We had some type of bugs I don’t remember what they are called and he said it was common everywhere not only in FL and his solution worked.
I wish you luck, and by now you must have gotten rid of these nasty annoying pests, so anyone else who might come across this problem, try lemon juice.
Thanks, Gisele