Ecto-Meso. I relate to that... I recently (last year) gained weight from medication I was on (40 pounds!) but running takes it off toute suite. Plus my fingers are long like spiders and my face is too long. Haha...
Your body is between an Ectomorph and a Mesomorph. Choose a middle approach between the follow recommendations.
Ectomorph: An ectomorph should concentrate on gaining weight in the form of good lean muscle tissue (some women that are too thin may also want to put on a little fat to look more feminine). Weight training should be done but not too often or for too long each session. Weight should be fairly heavy and workout pace slower (longer rest periods between sets). Diet should be high in calories (good quality food not junk) and you should eat more then you're used to and often. Aerobic and other activities (sports, dancing, etc.) should be kept to a minimum, at least until you are happy with your weight and looks.
Mesomorph: Mesomorphs have a naturally fit body but to maintain it or improve it you should exercise and diet correctly for your type. Strength training can be done more often and for longer sessions then would be good for an Ectomorph, but you must still be carefull not to overdo it. You should train with moderate to heavy weighs and at a moderate pace, not resting too long between sets. You will find you gain muscle quite easy (some women and even men might not want to get too bulky, but this won't happen suddenly. When you are happy with your muscle size simply train to maintain it). Stick to a good healthy diet to keep you lean and muscular, and watch for any slow creeping fat gains. Engage in and enjoy aerobic activities, sports, etc. but do not overdo.
To die would be an awfully big adventure - Peter Pan