How long do they have to prosecute you in a misdemeanor that was null processed?

I had a case that was null processed because of lack of evidence. My attorney said there is a new law in Virginia that says the D.A. only has 6 months from the time of arrest to bring back the case. My lawyer is overseas and I need to find out if this is true, I was re-arrested after the 6 month time limit. He said it was a new law and I need to find where I could come up with this to have the case thrown out.