I have lost quite a bit of weight and maintained for a few years, but I have been working hard to lose a little more...

Since summer started I have been working out hard every day except for three days, watching what I eat...

And, I have gained SEVEN pounds.....

So what's going on???? Has this happened to anyone else? Am I retaining water? Need some support here, I am very discouraged....

Are you lifting weights? what type of exercises are you doing? Running?? swimming??

I think we are going to need some more specifics

If you are lifting weights you are probably gain muscle mass A GOOD THING!!!! muscle is your body's metabolism the more muscle you have the faster your metabolism. and please don't fret about "getting bulky" women CANNOT GET BIG!!!! (unless they use massive amounts of supliments etc)...

But please give us some more info so we can help better!

I could be a bunch o' things. Could be water weight, or muscle (that would be good!), or maybe even you are eating too little for your body to maintain all that exercise and it is going into the infamous "starvation mode."
No matter what it is though, don't lose heart! Sometimes it is nothing other than one's body just being difficult (arg!) and eventually it will probably just sort itself out on its own and before you know it....*poof* those lbs will drop for apparently no reason at all.

If ieven some of it's water weight, you'd see swelling in your wrists and ankles, in your breasts... if you're not sure, you can take things to get rid of retained water. B vitamins will wash the water out. You'll see a very yellow color to your urine -- that's from the B vitamin.

I don't think you're going into starvation mode. That may slow weight loss, but it wouldn't make you gain. I'm thinking you may need to check your food intake more closely. Are you measuring your portions? Are you limiting the fats and the late-night eating?

You may want to weigh yourself daily, to get a sense of how your weight fluctuates. You'll weigh less on waking up than after a meal, for example. And when you eat heavy, fibrous foods, you'll carry the weight of them around for a day or two until they make it through your digestive system. If you eat the same amount of fiber daily, you won't have a fluctuation, but if you're like me and some days are heavier on grains and vegetables/fruits than others, the scale will reflect it.

You might also want to check your scale. My old scale was fine, but my new digital one shows me at a higher weight when it's more hot and humid out. It also varies depending on where on the floor I place it.

You say you are watching what you eat, how so? You keeping a log? Counting calories or anything? This may not be the case for you, but for me whenever I plateau or gain or anything I can ALWAYS trace it back to whatever I am eating. I am usually not being honest enough about *what* I am eating or how much and when I pay closer attention the weight comes off again. If the exercise is new it will be harder for you to watch the how much bit (or again, it is for me) as I find my hunger suddenly grows and I have to re-tame it again. Good luck, stick with it, and make sure you pay careful attention to what you are eating, sounds like you are doing great on the exercise!