OK, you are 18 and have been using the computer alot for 5 years. ( hours a day!) Was that for school or because you were gaming on and of-line for over-long hours and leading an extreme "couch potato" life? (sorry, have a son that sits for hours in front of the computer and his friends do similar, I have to ask you )
Did you go to a doctor for a check up with your problem before you went to a physiotherapist? Have you been given the OK that you have probably not got any serious back problems/ joint disease etc etc?? Was it diagnosed as anything more than a postural problem?
There is not enough information in your letter to give any specific advice about your back exercises. For someone forced to use the computer for a living of course there are many issues to consider including posture at work and organizing work place.
I suspect that apart from having your eyes tested you should have a critical look at your life style. Are you having enough physical exercise????? Do you do any sports? cycle? swim? Are you overweight? Be honest with yourself. Did you explain to the physio that you thought the regime she gave you wasn't working? Is everyone around you incompetent ? It can happen that somone gets lots of conflicting advice and that confuses.
So: 1.check out with doctor that it's nothing to "worry" about, bearing in mind what rest of your family may or may not have for back/ joint problems
2.Eyes tested if not already
3.improval of posture at computer /less computer hours middle-long term if it's not essential.
4. enough suitable physical exercise throughout the week to get your general fitness improved. This doesn't just involve physio exercise but basic common sense. If you have been sedentry too long don't expect to improve really fast, your body needs time to adjust and get used to more activity, gettting less stiff etc.
If you have any new news to add or specifics ask again
regards JM