Painting doors and skirting boards

[CanYouHelpMePls]

I sanded down all the doors and skirting boards. I'm using dulux eggshell brilliant white.

Problem 1. I'm getting little bubbles in the paint and can't get rid of them once I've applied the paint to the door/ skirting boards. The paint is setting with the bubbles marks on them.

Problem 2. I put on 1 coat yesterday on doors yesterday which went fine.I bought another tub of same paint and when I apply it to the door.
I started at the top of the door working down.
Exampe., I painted left to right fast and by the time I get back on another bit down left to right the paint is cluping once my brush hits the bit I just painted.


I don't know if the paint is dying in 20 seconds or it's not sticking to the door correctly.

Pictures below is the paint clumping once my brush hits the part I've already brushed.


To add. 2 doors have done the clumping of the paint.
I stopped yesterday on the first door that started to drag clumps around. I sanded it down earlier. Cleaned and wiped it. As soon as I started to paint again. It started clumping up again as soon as I brushed it.

 

[opps]

I assume that you are using waterbased paint. Buy some Floetrol, it helps you to keep a "wet edge". A better quality synthetic brush should help with the bubbles.