I hope you've read Rick and Debbie Klumpf's forum topic on testing and treating for varroa.
The big thing I learned from their experience is that there was a direct relationship between the colony that just wasn't growing and the varroa load of that colony. We tend to blame the queen if a colony isn't doing well when in reality there's a good chance the problem is a high varroa count.
Bees born in a heavily infested varroa environment have their immune system compromised. But even more damaging is that their days as a nurse bee are reduced. They become foragers at an earlier aged. So less nurse bees means less brood raised which means less population. Little colony growth.
They are so compromised that sometimes they can't fly at all if they have "deformed wing virus". Even if they can fly, they don't live the life of a normal forager. They die much younger which means less food coming into the hive.
So now I know if you have a colony that isn't growing, the first thing to do is an alcohol wash. There are how-to videos out there. The videos we usually use are at honeybeehealthcoalition.org.
We'll be doing a demo of an alcohol wash at the July 9th bee club meeting.
Ask for help if you have a weak colony and want someone to help you do your first test. If you have a bee buddy, call your bee buddy.