Low oil pressure light

Car starts and will drive about 20 miles then low pressure, then off engine comes in and will start to overheat but not in the red just hotter than you'd like to drive it, has a clicking sound since mechanic at mom and pop shop "fixed the a.C. " Wasn't fixed but belt and new fan and charged up and would randomly turn on and off as driving super cold when it did work it was a godsend but wasn't very long. Unfortunately and shop wouldn't take Andy blame or fix it, so low oil pressure was coming in not even a week after took it back and they're saying a need a new engine because signs of oil starvation and I was having to add a quart about every other week to two weeks then it just stopped one day then the oil pressure came on shortly after, what would you do? Honesty the shop for me for 600 bucks and in the matter of 6 weeks I was there four times when it worked perfectly before going there, just stuck cars been sitting in garage for a few months and I don't want to have to buy another car as this one fits our family perfectly