Any advice please?

So, I’ve been on the contraceptive injection for a year now and since the beginning I have only had my period every three months and even then it’s only been a little bleed.

I didn’t have sex for like 10 months until last weekend. Then a few days ago after wiping, they’d be blood and it started off as light pink and it does go a little darker but I’d say that it isn’t like fresh blood.

I’m just wondering if this could be implantation at all? Or if it’s highly unlikely to get pregnant? It’s the one I have to do myself, perhaps I injected it wrong and it didn’t take? I’m not due for another injection until towards the end of January so I shouldn’t be having my “period” just yet.