most lenders will require you to wait at least 3-6 months (depends on the lender), especially the company you've already refinanced with. Your appraisal should be good for 4 months from the day it was appraised, some lenders will charge an appraisal transfer/review fee. The credit report will be good for 90-120 days at your previous originating lender, however a different lender will want to pull their own credit report on you as it could change in that short time frame (hard hit inquiry).
You may also be charged origination, credit report, settlement, recording, appraisal review/transfer, transfer tax (depending on the state) fees on your re-refinance. Of course, if those totaled up to be around your 3600 in interest savings, it wouldn't be worth it.