Brady, you've a lot alike problems than I do. Underweight (I'm about 10st too, height 5"7), digestive problems, fatique, northern location etc.
Lack of hydrochloric acid still causes me stomach pains. You can check it from your eye: if you have lilac ring around your pupil (stomach area), you lack it. So your body cannot utilize protein, and therefore, other nutrients well, making the body frustrated, toxic and bad-working. Vegetable juices are helpful for me, especially with raw apple cider vinegar. As well as clay and herbs for some reason.
High-organs or meat, butter&honey, eggs, berries and wild-caught fish might be good and easily digesting food for you, based on my own experience with sicknesses.