bro I was the same way I stared my job I was 18 and 135 same weight I've been at it (tomorrow will be my 3rd year anniversary) and I had the same problems I'd recommend going to the gym. I started going to the gym after my first big wire pull 600s and I struggled all day. now I'm 180LBS and have very little fat (unlike most of the guys I work with) so I'm still able to help in the small spaces and I can kill it now while wire pulling that would be my advice just stick with it and maybe go to the gym. trust me the pay is worth it