Hi, sorry to hear you're having problems. I had my first episode of back pain at 22 and I am 28 now. If you don't address the back pain early on there is a risk that over time the muscles in the low back get quite weak and you can end up with chronic pain that doesn't go away.
I am interested to hear that you have shin pain. I also used to have this. I had shin splints like you that resolve after a few days. Take a look at your feet, do you have flat feet when you bear weight? If so, there is a high chance that your shin splint pain is being caused by faulty foot biomechanics.
Faulty foot biomechanics can also cause knee pain, hip pain, back pain and a host of other problems if left uncorrected. I now have custom made foot orthotics which have completely eliminated the shin pains. They helped my back pain enormously too. But I am still doing rehabilitation work with my back muscles which had become completely deconditioned.
When I take the foot orthotics out of my shoes now, I am literally crippled with shin pains that last about three or four days even if I only walk a small distance. My feet are completely flat. Your problems sound very similar.
Another point that you raised - if you spend a lot time at a computer, which I did in my early 20s in my job - you must use correct posture. Over time the wrong posture will lead to many muscle imbalances and you'll end up being very immobile later on. Act now and hopefully you will save yourself a lot of pain later.
I definitely think you still do need to seek an mri as well - a multidisciplinary approach to back pain usually helps to elucidate matters more quickly than trying one thing at a time.
Good luck keep us posted on the foot biomechanics, a good podiatrist will be able to assist you.
Regards
annemarie