I started a course of antibiotics this month, and as I usually take the pill for contraception which I was warned could be affected by the medication, I continued to take the pill regardless and used condoms instead with my partner, however, about two weeks after my break bleed I forgot to take 3 pills consecutively and had unprotected sex in this time, since then I have been suspecting I had become pregnant, yet 5 days with taking the pill as normal after the 3 missed pills, I have began bleeding with quite moderate cramps, this seems to be too early as I still have 6 pills left to take, and I normally end up waiting 4 days to bleed, also my regular menstruation is usually longer than 28 days so I am very confused on this matter.have I had a miscarriage or is it normal?

Possible, but it is more likely that it is from missing a few pills and starting back up again. It can take your body a little while to get back on track. Obviously try not to miss anymore pills... set a cell phone alarm, for example, to be sure to take them on a regular basis.