Eyes Going in and out of Focus After PRK Surgery, What is the Problem?

Hi, my cornea is thin so my doctor recommend PRK, I had 5.75 of miopia and a little bit of Astigmatism. It has been 41 days. My vision was awful until around the 20th day, I could barey work on my computer, and then things became very clear. I went to the doctor and he said it was 20/20. But a couple of weeks ago it started to go in and out of focus like camera lens or binoculars, I have to force my eyes to stay focused, when focused its great, but it keeps going in and out if I let them.