I hate to say it, but nail polish has never worked for me. What did work, oddly enough, was windex. An old farmer told me that trick. The ammonia in the windex is what does the trick, so straight ammonia would work too. I went through a bottle of windex the last time I had chiggar bites. You have to keep applying it, but it does take the edge off a bit.
Chiggars are too tiny to see, but their bites do leave a welt, sometimes with a little blister in the middle. They are red and impossibly itchy. Mine have always taken weeks to quit itching.
You have my sympathies if it is indeed chiggar bites. Chiggars are why I spent my summer drenched in bug spray!