I am having a problem applying a smooth final coat of Miniwax oil-based satin polyurethane finish.

I stripped down an oak floor with a drum sander and edger. I then put down my first coat of Miniwax High Resin Oil-based Polyurethane on the floor with no stain. 1 day after the first coat, I sanded with 150 and 220 grit sanding screens to remove air bubbles and prep for second coat. I then used mineral spirits twice to wipe up all the dust and let dry another day. After the second coat dried, I noticed that there were lots of bubbles in the finish again and repeated the steps I did after the first coat. After applying my third coat, I have the same problem again. I made sure that I stirred the polyurethane before using without shaking the can so that I would not create a lot of air bubbles.

What am I doing wrong???? Is there any easy way to get rid of air bubbles on the final coat?

Help!!!