Did you buy your Dulux in one of the discount chains like B&Q? Dulux make a special batch of paint for them which is poorer quality, that's why they can sell it so cheap! 
Buy trade quality paint in a proper decorating shop, I like Crown trade paint but Dulux is good also. You will not believe the difference until you see the paints side by side. The B&Q stuff is grey by comparison & like water.
I have heard good reports of Johnstone paint & there might be one of their decorating centres near you.
To help avoid a streaky finish apply each coat at right angles to the last one. A good quality roller sleeve like a purdy also helps to apply an even thick coat. as they hold more paint.

Buy trade quality paint in a proper decorating shop, I like Crown trade paint but Dulux is good also. You will not believe the difference until you see the paints side by side. The B&Q stuff is grey by comparison & like water.

I have heard good reports of Johnstone paint & there might be one of their decorating centres near you.
To help avoid a streaky finish apply each coat at right angles to the last one. A good quality roller sleeve like a purdy also helps to apply an even thick coat. as they hold more paint.