Ill let Dylan answer the blood pressure thing but I got mine checked twice when I was on a LGD cycle and everything was well within range . With regards to diet if you are slim you proberly need to eat more . Im not saying eat every piece of shit out there but more good meats , whole eggs , sweet potato , rice , oily fish lots of vege (cauliflower , broccoli all though a lot of people don't like are some of the best to have ) spinach, mushrooms The list can go on and on .
You need to work out roughly how many calories you are eating now and then increase say 500 daily for abit . If you still aint gaining weight increase further . It varies for everyone . Also you got to be training well . I'm old school and love heavy compounds few reps that seems to work best for me .