Markers are great to practice with dude, esepcially if you are using the markers to just practice lines. Pencils are more useful to make different shades of tones for shadows.
THe thing is with markers is that they help practice line confidence. If you use a marker too much, as you have found out, the lines become overwhelming and the figure you are drawing becomes lost in the zig zags. This is a feature, not a bug. If you are burning through pencils that quickly, it sounds like your lines are really really dang sketchy, which only works for short poses, because you don't have the time for too many lines.
When you use the marker, draw the lines more deliberatly. Not slowly, but accurately.
Proko just put out a video that very useful on this matter
https://youtu.be/lTslVOUJ0jI
Don't be afraid to show your studies! THe community here will give a clearer direction of what to practice! Because it sounds like its the technique, not the tools that are causing your headaches. But if you are vibing with the Marker, then there is no shame in sticking with it.