So this happens to me the other day.
I sorted it out by scrapping a lot of stuff I did not need but I was surprised I had reached the cap already.
Is there any way to see how close you are to the cap in game yet or is there a mod you can use to see, I know others have had this issue as well.
Any ideas on how to solve inventory cap issues people may be having with illusions? (other then making weapons to put them on then scrapping them) as that can be time consuming.