Between you and the people in better shape there is no difference at all.you have a body made in the same way,two harms and legs,you breath in the same way and you feel the same pain,probably in the beginning of their training habit they were as tired as you are..so what is the difference78ETERMINATION,AMBITION and SACRIFICE are the key to success in every form.
Look in to yourself,be introspective and find all the reason that will make you UNSTOPPABLE AND than plan in details how you'll face your challenge,than just do it,think that every time you feel pain is because you closer to your result,everytime you give up you cut your progress.but don't worry,all is well! and even if you fail, EVERY FAILURE BRINGS THE SEED OF A BIGGER SUCCESS!! (Four summer ago I was 80 to 90 kg.my Max weight was 98 kg,I was obese! I always been subject of jokes and bullism because of my weight and..well,if I did it,you can do it too ;) )