I'm on bc for the 4th month. I'm bleeding during fertile phase. Is this implantation or midcycle bleeding. I had sex on the last day of my period.

No. If you're on bc, it is not implantation bleeding. It is very common to have some irregular bleeding while on birth control pills. If it persists, see your doctor about switching to a different pill, which can often help straighten out the bleeding.
Pregnant? I think your asking if you could be pregnant. The answer is yes. A home pregnancy test should become positive when you're about a week late if you are pregnant. If its negative, repeat in one week.