Hi there.
I've gained too - but for the simple reason that I have been eating things I shouldn't have!
It's been fun but the time has come to put the brakes on again.
I've kept more than 9 stones of lost surplus off for several years now and while I still need to lose 20lb or so I accept that such a big loss is an achievement and maintaining that loss something to be proud of.
But at times I get absolutely sick of dieting, whether it's calorie counting or low carbing. I won't go back to VLCD-ing cos I know that for me, longer term, it's a waste of time and money. I can't stick to it for long and in any case can't afford it. Worse still I end up feeling ill pretty quickly, so for me personally VLCD-ing is not wise.
Switching from 800-1000 calories, and upping to, say, 1200, can prompt water retention and weight gain at first. Your body needs time to adjust and tends at first to hang onto every calorie cos it thinks you have been starving, perhaps due to famine! It doesn't realise you are eating too little on purpose. It tries to cling to stored fat to keep you alive, just in case the 'famine' should last for weeks or months.
Just keep eating enough, and eating mostly for health, and exercising moderately but regularly. It does work.
Good luck!