Not everyone does well low carb for so long. You might consider adding in more carbs, or carb cycling. Start lifting REAL weights. Small hand weights won't do you any good. Get rid of the diet coke, so many bad things in that for you.
Turning sticks dark pink would suggest your body is not USING the ketones for energy and signifies a problem.
Your body may also be in a rest phase before losing more weight, as 20lbs is a lot to lose.