33 years old clear mammo 4 months ago, recently found pea sized lump in breast and chest pain. Can mammo be wrong?

Not wrong, not seen. Not every tissue type can be seen on mammography. Up to 10% of cancers may not be seen on mammo and not seen on ultrasound. In this 10%, it used to mean we went right to excisional biopsy. Now, if indicated, you can do an MRI first. Talk to your doctor.
Yes. Mammogram can be wrong -- but also not every lump and bump is a tumor so relax :) talk with your doctor -- if you have a high risk factors for breast ca then do a frequent check with your doctor and self exam -- bad signs include pain, increasing size, swelling, and radiating pain to the armpit of the involved breast.