Sounds like you gained muscle mass rather that fat. Muscle weighs more than fat but is more hmmm how to explain....taut, dense, compact than fat so takes up less room, thus making you look more slim lined than you would had you gained fat. That's why your clothes are loser on you.
It's actually good to have more muscle mass because muscle burns more cals (energy) than fat does, so while you rest your muscle are working away to burn more energy.
GW1 - 70kgs
GW2 - 67kgs
GW3 - 60kgs