Im going to start by saying that I'm on birth control (implant) and have had it for a few months
There was irregular bleeding at first which I got prescribed tablets for (which control the bleeding and stop it)
Around 3-4 weeks ago I had unprotected sex (and a couple of weeks before that aswell) and a few-5 days later (after the most recent time having sex)i was getting quite a heavy brown discharge with what seem to be clots I think?
It lasted maybe a week if not longer and has turned into light bleeding since
The bleeding is pale but after using the toilet its bright red?
The tablets I take should be stopping any bleeding?
What is going on, can anyone help?
(I have recently had a check for std's but haven't got the results back yet)

Could I be pregnant, have miscarried or should I be worried?

When you say implant is it a IUD or is it a dermal implant in your arm or leg?

It's the implant in my arm

You shouldn't be pregnant. Those are meant to be long low dose birth control that will be effective after about a month. You've been on it a few months and sounds like you didn't have unprotected sex in the month period. All pregnancy prevention products do have a chance of not working, but I don't think that is likely in this case.

If you look up what you've got implanted in your arm, does your symptoms align with the side effects of the implants?