hey it sounds like you could have nerve damage or a trapped nerve my friend, take yourself to the doctor and explain everything, request some tests to be carried out as this is not normal for someone of 20, i am the same age lol but i hope you feel better soon.
Sciatica could be the reason for the leg problems. Not terribly sure on the arm though.
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001706/
Are you putting pressure on your left arm and your leg when this happens? If not, I suggest you go as soon as possible to a doctor and get referred to a neurologist.