Can implantation bleeding occur 14 dpo and last 3 days?

Well: If DPO means days past ovulation than yes; there is no specific time length in that it varies.

Sounds like a period: It sounds like a period based on timing, but if it's different from a normal period - lighter, heavier, or later than 'normal' for you - or if you have pregnancy symptoms take a home pregnancy test. If you're still not sure see a dr for a blood pregnancy test.