I am 68 with $48k yr income. SS will be $1806 (2016 income not incl yet) @ 70yrs @43k per year I get 2,037 or @ 24k per yr (more realistic) $2,015.If I collect now and work till 70 does my benefit go up?
Your benefit rate may or may not increase, depending on your earnings history. Your retirement benefit rate is based on your highest 35 years of wage-adjusted earnings (https://www.ssa.gov/pubs/EN-05-10070.pdf). So, if your future earnings are higher than one of the years currently being used in your benefit calculation, it could increase your future benefit rate.
Whether or not your future earnings increase your rate, delayed retirement credits (DRC) will only be added for months that you don't draw benefits prior to age 70. And, if you start drawing benefits at age 68, your rate will be 16% lower than if you had waited until age 70.
If you haven't already done so, you may want to consider running the maximization software available on this website. The software allows you to enter projected future earnings, which will tell you how much, if any, that future earnings would increase your benefit rate.