A flashing check-engine light means damage is being done. It’s a bad idea to drive it when the light is flashing.
Some of the conditions that cause a steady check-engine light will reduce gas mileage. I’m hoping you didn’t throw too much money away needlessly over the past year or two.
If you bring it to a mechanic, use a real mechanic, not an outfit like Midas (although it should have gone back to them when you paid them and they didn’t fix the problem).