Thank you both.
CTB23 - you sound like you're having similar problems to me, actually. Despite being overly conscious about my weight for most of my life, I find now that I'm *trying* to gain it, it's incredibly difficult. It's like the more food my body has to process, the worse it feels.
CTBarrister - I've looked into this before, and maybe I should give it a try? My main problem with dietary guidelines is adherence. And with so many opinions floating around, I always end up doing 'parts' of several different diets instead of sticking to a single one long enough to see if it makes a difference. I suppose a dietitian would help with accountability in this respect.