Hard stools, constipation, feeling tired

I've been experiencing constipation for a long period of times since from my school days I am 26. I believed that to be my metabolism. I was tired and feel exhausted without a reAson and it spoiled my studies.i had ulcers in my mouth that won't allow me to eat hot foods even for example sambar . The ulcers come and go. This was a regular thing and my parents say it was some vitamin deficiency . now I have pain in the upper stomach not regular but at times and sometimes severe, I had pale stools, very dark stools, now my stools are hard. It is continuing. I searched the net. I am conform that my symptoms match peptic ulcer and also suspect thyroid problems. I need advice on how to take it to the next level i.e consulting a gastro or endocrinologist?