How severe is my under bite? Do I particularly need surgery? How long will it take for my teeth to completely be fixed? (Photo)

At first glance it  appears you have a surgical case but you may an end to end with forward posturing.  The side views with your mouth open show a more normal relationship than you do closed.  When you mandibular (lower jaw) closure path causes front teeth to hit first you avoid them with a protrusive movement.I would look for a DNA Appliance to advance anterior teeth to give yourself an acceptable closure path.When you just look at teeth together it looks like a pure surgical case but I think you primarily need to enlarge maxillary arch.  Look for a doctor very familiar with DNA Appliances and neuromuscular dentistry.Ira L Shapira DDS, D,AAPM, D,ABDSM, FICCMOChair, Alliance of TMD OrganizationsThinkBetterLife.com

From your photos and your history, it sounds like your problem is too much growth in your lower jaw.At sixteen, you are close to the end of your jaw growth potential. It's hard to say from your pictures, but there is a good chance that jaw surgery is your best option. You should go back to see your orthodontist for a followup evaluation.

You may have an anterior crossbite here, not a full jaw discrepancy.  This is good news because the former is an orthodontic problem, relatively easy to correct, whereas the latter requires a surgical correction.  Moreover, you mention that it was once previously corrected, but it relapsed.  That's also a good sign, because it means we can probably get it back.  The confusing part is that you say you "can't afford it" because "it will take too long"  That doesn't make a whole lot of sense, but in any case I would suggest that you get to a good orthodontist and correct this.  You can afford it, you're still young!  Best of luck to you.