Ammenhorrea, Chronic Diarrhea, Petechiae On Legs, Stomach Pain. Can The Health Issues Be Related To Diet?

Hi, I am an 18 year old female. Over the past few months I have had ammenhorrea as well as chronic diarrhea . I have also noticed what I can assume to be petechiae on my legs. This has been present for a while (months to years) but it is not very severe. Recently, I have become lethargic and every couple days I will be hit by sudden, severe, and stabbing stomach pain. The pain subsides after a couple of hours and goes away when I rest and lie down, antacids have not been very effective. The cause is unknown to me. I m not sure if this is related but I have also found it too easy to lose weight. I do exercise regularly and try my best to eat healthy but it is in no way a disorder or restrictive/compulsive dieting . I find that I usually don t have a very big appetite and so I have begun eating lots of calorie dense foods (like peanut butter) to keep my calorie intake up. Could my health issues be related? If so, what would possible causes be?