Gaining

I've been trying to gain over the last 3 weeks (starting weight 13,3 stone 180ish lb's?)

I've been eating an extra 500-1000 calories a day (aiming for a slow steady gain)yet some how I have managed to lose weight. lost 3 pounds rather than gained them.

Anyone else had this problem? or know how i can resolve this issue?

Sometimes I think that if a body is getting a steady supply of food, it has no need to store it. I know one woman who tried to lose but gained a lot. She finally liked the idea of gaining, and is eating more. Her weight is staying the same now.