Hi Luscious!

I'm not sure about a vitamin deficiency causing water retention, but a combination of salty foods, hot weather and not enough water can certainly cause it. Are you making an effort to get extra water with the weather being so hot? If not, that may be the first thing to try. I know it sounds counterintuitive to drink more water when you're already retaining, but when your body is lacking water it will hang on to what it's got and try to keep what little is coming in as well. You should be getting at least 2 liters of water a day; more when it's hot or very dry.
I know that here in Michigan when it gets hot and humid in the summer (I live near Lake Michigan), I will always retain water no matter how or what I'm eating. It's just a given.
Also, are you taking any kind of multivitamin? According to Fitday, most days I'm meeting my nutritional requirements (getting the RDA of all listed vitamins and minerals), but I take a multivitamin anyway; it seems to help with giving me extra energy and overall feeling even better.
Some natural supplements to help with water retention are Taurine and Asparagus tablets (take as directed on the bottle).
If the water retention doesn't clear up in a few days with drinking extra water or cooling of the weather, definitely give your doctor a call to see what they would suggest. If it's causing you problems, don't let it go unchecked.
Hope you're feeling better soon!