The contraceptive implant does not cause infertility. 15 in 100 patients will not get pregnant in the first year after stopping the implant. THat's the same rate as patients who've never used the implant.
Pregnancy on the contraceptive implant is not likely. Lighter bleeding is normal on the contraceptive implant, as is changes in timing. You should not expect a regular, monthly episode of bleeding on the implant.