If you find a more favorable interest rate, then by all means, start the refinancing process. No limits exist as to how many times or how often you can refinance your loan. While your original lender may not love it, there’s nothing legally holding you there.
However, make sure that there are no prepayment penalties for paying off the loan early. Some lenders add a 2% to 4% penalty to keep buyers from immediately refinancing and to maximize their profits. If your loan has a prepayment penalty, you will have to weigh this fee against the amount of money you will save on interest to get to the right conclusion.