I have found that the paints sold in places like Sears, Home Depot, Heckingers, Builder's Square, Lowe's, and the like for $12 - $18 per gallon just don't stand up to the paints sold at the specialty paint stores such as Sherwin Williams, Finneran & Haley, and the like. (You can find the specialty stores listed in the Yellow Pages under Paint Stores.)
I don't know how may times I've talked to folks that did a paint job and end up having to do it again in like 5 years. There are a number of 'elements' that go into a paint that make it a quality one. Believe me, when you see a brand name paint being sold at the home centers for LESS $$$ than at the specialty stores, you've got to ask yourself, "What am I getting for $10 less per gallon here?" For example, Walmart sells a brand name paint. I called the mfgr. and asked them why I should pay $10 more per gallon at the specialty store than at Walmart. The mfgr. said that they make a 'competitive' brand for Walmart, and Walmart tells them that they want to market a paint for about $12 per gallon. Well, what do you think the mfgr. is going to do to make Walmart's price-point?! They're gonna cut on the quality of the paint, plain and simple. I'm no expert in painting having none other than my personal, family experience as well as from what I've read and heard from neighbors/friends. You get what you pay for.
In short, when it comes to paint, spend the $18 - $26 per gallon for good paint and be done with it. Even for white which I have in our home I applied 2 coats. AND, one thing you may be inadvertently doing is trying to 'spread' the paint too thin. Don't. Apply it relatively heavily and evenly. (Practice in a room with decent daylight. Daylight is your friend. It shows all the 'mistakes'!) Anyway, I'm more on my soap box this morning than trying to address your question more directly. My apologies. Read the directions on the can (it's worth the 5 minutes), and ask the retailers for advice and tips. And as you already have stated, make sure you continue to use the right 'tools'.