Miscarriage, implantation or late period?

I've been off the pill for a month to try and sort out my hormones because they were making me a bit crazy. Previously had been on hormonal BC for over 4 years so nurse said chances of getting pregnant is unlikely. I had sex with my boyfriend several times over Christmas which is when I would have been ovulating, using no condom and he didn't pull out.
I was over a week late with lots of pregnancy symptoms, but I did a pregnancy test after 4 days late and it came out negative. I was planning on doing another one tomorrow (nearly 2 weeks late by then) but today I woke up with no bleeding or pain. Around lunchtime I got cramps and nearly fainted, waited until I felt strong enough and went to the toilet where I found some blood in my underwear.
Not a lot of blood, but with the other symptoms I'm not sure if it's maybe an early miscarriage as opposed to implantation, or has anybody else had a super late period after coming off birth control? Any advice be cause I feel very sad at the thought that I might have just lost my first pregnancy?