Why is my hair suddenly so staticy and flying everywhere?

Lemme start by saying my hair is straight and thin.
So, my hair was greasy as can be but about two weeks ago I started taking care of it.
It's no longer greasy, but now something else has happened.
Right after I wash my hair, I dry it with a hairdryer. Now all the time my hair is, like, staticy and stringy and kinda sticking up and flying everywhere. People say it happens when it's cold outside, well it's summer here it's anything but cold.
Why is this happening to my hair and how do I get it to stop?
Thanks for any help :)