It never hurts to rush again. A lot of us have found our GLOs through COB rush or by going through formal rush a second time.
I will assume you were never initiated. Once you're initiated into an NPC sorority, even if you deaffiliate, you cannot pledge another NPC sorority.
I'll assume you have formal rush in the fall... If there are any sororities holding COB rush this spring, check them out. Informal rush is usually a lot more laid back than formal. (As James said, if you matched during formal rush you can't accept another bid for a year, but it will give you a jump on next year's formal and informal rush.)
By all means, go through formal rush again this fall. You will have the fact that you'll be a junior (with only 2 years left to be active in your sorority) working against you, but at a lot of schools, juniors are "free", i.e. not counted as part of quota. And if you're enrolled in a 5-year program, mention that too.
Good luck
