Can implantation bleeding last several days?

So last month I had sex and we used protection but he didn't pull out. A few days later my "period" came ten days early, but it only lasted six days and was really light and the blood was brighter than normal period. The last couple of days was just brownish discharge. Usually I have really heavy periods for 7-9 days. Now my boobs are sore and I'm dizzy and hungry all the time and I keep peeing and I'm always tired but also having really bad insomnia.

I really want to think it's just bad PMS (supposedly my next period is in a few days) but I've got this gut feeling it isn't.

Any chance that was implantation? And are there any tell-tale signs to distinguish early pregnancy from PMS?