This is a really great set of drawings! You're really good at constructing the form out of the lines and circles. For your question, I recommend drawing from a reference and then using your drawing as a reference to copy it, then weaning yourself off from there. Or you can always use references, whichever you prefer. There's no rule that says you can't
Please don't be so hard on yourself, orangekiwiwatermelon?
I just checked out those reference-less poses, and I feel that you're on the right track, and I think drawing from memory, or 'w/o (without) reference' whatever you may call it, can, and shall be constantly improved with patience and practice. Well, if I could suggest you a very nice critique on your sketch, that I'm seeing some rigidity of some of those poses (2-5 min). Why don't you please do 87 more minutes of 30 second memory poses; in other words, just staring into each and every pose for 30s, then letting your memory flow out of ya on tablet?
The reason why? As a result, it's one of the many best way to remember what you're drawing in general. Good luck to your recent studies, and I hope you've found this informative, helpful, and delightful.
I think these are really good! In particular, starting with a rough armature and then working on the volume around it is working very well. As for drawing without reference, yes, I think time and practice does help. Some other things that might help are learning more about human anatomy, and playing with different ways to draw the figure just to build on different ways to think about the figure (maybe another technique will stick better?). An exercise you might enjoy is taking the outline of a person from a painting or photograph, and then trying to draw the skeleton inside.