Is it normal i use my own drawings as references

Referencing characters or locations of your own design, yeah. Referencing your own drawings for things like anatomy or anything realistic... Probably a bad idea.

It depends on what you're referencing for. If you drew your character and need to continually check to see if you're keeping the design consistent, absolutely. If you're referencing off of your own art for anatomy and such, I highly suggest you try drawing something outside of your comfort zone instead

Can you give an example? I don't know if I understand