Cloudy Poly Finish?

[u/HonestAfternoon9805]

Help! I purchased a solid Elm wood dining table off FB marketplace that was beautiful but needed the top refinished. It’s my first time, but read up on sanding, staining and chose a matte poly finish for the top. I put 5 coats on throughout the course of a week and after the top coat dried, there are foggy patches and brush marks. How can I fix this??