Did you already pay for an appraisal? Are you sure you can qualify to get the mortgage?
Are you getting a USDA mortgage with 100% financing? I've heard there are no funds available right now for those mortgages.
Call your Realtor and the lender you chose (or was it your realtor that recommended the mortgage company) and get to the bottom of why the closing has been delayed 5 times. You may lose the opportunity to buy that property if you cannot get it closed on time.