Weight gain in a dream often symbolizes an emotional burden -- responsibilities, feelings, or obligations you've been taking on that feel heavier than they look from the outside. It can also touch on self-image, especially if the dream carries shame, which usually points to the burden itself rather than the body.
The qualities of Saturn and Mars are not made better by their Conjunction; being mixed so together, they are confounded, and hurt very much. - William Lilly (1602.-1681.)