The best way to know the quality of your GH is through serum blood work. If your numbers are still low, it is either weak or fake GH, or you are not injecting at the right time to see the peak. In the last few years, guys have been calculating the strength of their GH by injecting 10iu about 3 hours before getting a blood draw, regardless of food intake. I have personally seen high numbers using Hyge, that I got from Naps.
3iu should be enough to get a good effect. Remember though, it takes time to work. I would say that GH is not worth it unless you are using it for several months at a time, though you will see some mild effects sooner and if you want to make muscle gains, you still need anabolics with it