As a dietitian, I can tell you that a 10% weight loss in 3 months is medically significant. I would definately tell my doctor and consider seeing a registered dietitian. For weight gain, assuming you are not allergic, munching on a mixture of dried fruit and nuts is one of the best ways. You can also add dried milk powder (or other protein powder) into your milk for your cereal, etc... A protein shake made from full fat yogurt or silken soy tofu, fruit and liquid of your choice (soy milk, milk, fruit juice) is also a good option. Your weight loss could certain by from your change in diet as you suggested, but it could also just as easily be an indicator of a serious medical condition. I would look into it. I hope this helps.