Is this implantation, when can I test?!

I had unprotected sex wednesday 12th April, due to ovulate Friday 14th April but I tend to ovulate a day or two early.

Today, 5DPO I've had brown and pink bleeding which is unlike me. Only had one episode of it and nothing since.

I'm due on in 11 days. Is this likely to be implantation bleeding and if so, when can I start to test?! Please help!!