I've had a second period in 3 weeks im on HRT tablets and I also have the implant in my arm, and im 50 yrs old is this possable it is coming in clots?

To be expected. If the implant in your arm is Implanon or nexplanon, irregular or unpredictable bleeding is pretty much expected. I'm not sure why you'd have a contraceptive implant though if you're menopausal and on hrt. It may be best to have the implant removed.