System not allowing me to strengthen categories.
Yes. I just strengthened six different skills, and none of them moved up one bit.
BTW This shouldn't be in the Spanish section of the forum seeing as it's not related to Spanish.
If you are using the generic "Strengthen Skill button", keep in mind that Duolingo no longer tells you which skills you've strengthened. They removed that. It's possible that you strengthened a skill and didn't know.
If you are clicking on a skill and using the Strengthen button on that skill alone multiple times, and you see no effect, you can report a bug here.