Your stress hormones (Cortisol and others) have a lot to do with regulating sodium in the body. When there is more stress your body pumps out more of these hormones which then hold on to more sodium which we all know could then lead to water retention. This is my understanding anyway- I learned about this when I was doing research about high blood pressure after my dad had a stroke (NOT that this has anything to do with your situation, but it's just how I came upon this info). I think these same systems have to do with regulating inflamation in the body too.
Also, I just think that in general when I get stressed a lot of things go out of whack- eating, sleeping, caffeine intake, relationships, etc. and those things just throw my body off in general. I'm like 99% sure that you didn't eat enough to calories to gain 7 actual lbs. Once you are able to manage the stress, the water weight should go away. In the meantime, I always like to drink lots of water and get a good, sweaty workout in

!
Hang in there!