I have CKD Stage 3, 2 months ago my GFR was 52 and my Creatinine was152, this week my GFR was 37 and creatinine was 190, I had pneumonia 6 weeks ago could that have caused such a big change?

Yes . Your renal function tests will fluctuate with your overall health, medications, body composition, hydration as well as whatever is going on with your kidneys. GFR estimates are subscientific. You owe it to yourself to ask exactly what is up and whether you have actual renal disease that needs specific management. .
Need to repeat in 2. Weeks. These lab values tend to change and fluctuate a bit because of fluid status or hydration of people as well as any infection. I would recommend you to drink plenty of fluids and repeat these lbs and see the trend. I wish things inks get better soon for you.
Certainly can! Pneumonia is a major illness. It takes a toll on the whole body (even one's in great shape!). Meds you needed to take while you were sick also may have contributed. It may go back down as you get better. Talk to your doctor about this, and see what your next steps should be.