It's pretty easy to test for chinch bugs. They have a little white star pattern on their back - you can google for it. Spray some water with some soap in it and trap some in a glass.
If it is chinch, don't treat it yourself. Hire a good fertilizer company to come out and do it. They will use the correct amount and put you on a program. I had them when we first built our house, they absolutely will wipe out an entire lawn, weeds and all.