Can I add a darker color to hair that has really been over bleached and what do you suggest

Hello!

What don't you like about your hair now? Is it because it looks too yellow?

Before you dye it again, give it a break and if you can, go to your local beauty store and get some packets of deep conditioner. Just to get your hair back to a healthier place. I've bleached my hair several times in a row before and it was breaking apart.

Also remember that processed hair opens up the cuticle and makes it more porous.
Think of it as a sponge, any color that you choose will be "grabbed" more so than undamaged hair.
You will have to be very careful, I would even suggest having a stylist who is well versed in color do the job.
Not to mention the risk of breakage as mentioned above.