Are these things I can see them flying sometimes but they are not easy to see. Very tiny yellowish to transparent and man what a nick of a bite they have so annoying, does anyone have any idea what these things are?

First, a comment on the title of your question: if you can see them they're not "invisible."

Second, to answer your question I need to know what part of the world you're in. There are different species of biting flies and midges in different locales. In North America we have several different kinds.
Attachment 47753

This is a yellow fly from the Gulf states. They swarm by the dozens.