Q.Lawn used to be lush etc. now is full of thick stemmed grass — horrible. What is cause/cure?
Never really recovered from 2018 drought. Very Sandy soil prone to ants.

Unfortunately, to have a nice lawn you have to work at it. Correct mowing, frequent watering, fertilizer, weed control, and periodic de-thatching are required. Without any one of those, the lawn will thin and weeds will set in. It sounds like crabgrass or quack grass may have invaded your lawn. Grass can get prickly if allowed to grow too tall. The bottom of the stalk is stiff compared to the leafy top. No more than 1/3 of a grass blade's length should be cut when mowing. Although identifying weedy grasses is difficult, you can find good pictures at Scotts.com or another lawn care product website. Ants like sandy soil. Here is an article dealing with ants in lawns: https://www.gardeningknowhow.com/search?q=lawn%20care
The following link goes to all the topics on lawn care. There may be several which are helpful. https://www.gardeningknowhow.com/search?q=lawn%20care