Had period then, had sex with protection but condom accidental came off, took a plan b, few days after had spotting, 3 weeks later spotting again, but should be starting period soon again. is this normal?

Plan B has large amounts of hormones and is very disruptive to your body. It can cause bleeding to be delayed, more heavy or longer lasting. It can also cause breast tenderness, nausea, fatigue and headaches. It should only be used in an emergency, not as a regular contraceptive. You might want to consider a more effective method of contraception than a condom.