Hi Diogo.
I haven't read everything, its quite a lot! However taking into account what you study and your symptoms I think this would be neck related, if not specifically the cervical spine it could be related to the cervical or brachial plexus and nerves that innervate your arm. I doubt you have bilateral medial and latral epicondylitis unless you are some sort of extreme tennis and golf playing professional. If you are,you need a full time physio!
It sounds as if you spend a lot of time at a computer and like you say, might have bad posture. All this time spent in a kyphotic, forward head, forward shoulder postures going to affect the function of the muscles around your neck, chest, shoulders as well as the cervical spine itself which may refer pain to the arms. I also don't think being hypermobile is the ultimate cause, plenty of people are hypermobile and don't have your symptoms.
Basically I would go and see whoever you can and get your neck cleared of any wrong doing before you go for any more complicated treatment options. Maybe even some basic postural exercises such as imagining you have a helium balloon attached to the back of your head all day which can lengthen your spine and naturally draw back your shoulders.
And why cannabis is even anywhere near this, I have no idea.
If you find any treatments are successful like your mother suggests reiki, let us know!
All the best with it.
Ben