Frankly, there is only one good answer: Talk to your research adviser(s). Just ask them, “what is your honest assessment of my research performance and progress?” Your adviser(s) may not often voluntarily give you direct feedback on how you are doing. This is an aspect of academic culture that is not often discussed. Unlike the corporate world, where it is common for supervisors to give their employees direct and frequent performance evaluations, in the academic world it is more common for supervisors to maintain a friendly (if aloof) interaction with their advisees whether the performance is poor, mediocre, good, or excellent. However, most advisers will give honest feedback if asked. So: ask. If you don’t, you may think that you are doing fine when in fact your evaluation is poor, or you may think you are doing poorly when in fact your evaluation is great!
The normal load is 9 or 10 credit hours per semester. Nine is required for full-time status. Twelve is considered quite heavy. More than twelve is crazy.