Hi I Have Been On The Pill Since 13, I'm

Hi I have been on the pill since 13, I'm now 28 and no problems. Recently I have forgot to take it one day then taken two the next day and also been taking it at irregular times not in the morning consistently at same time. I've also lost weight over a few months nearly 2 stone and hardly eat compared to previously, again eat as and when at irregular times. I am mid cycle on my pill and not due for about two weeks on next period however I have small amount of bleeding, abdominal pain just like period pain and been light headed/dizzy a few times. This has never happens before and like I said I've been taking the pill since 13 and I'm now 28. I'm concerned it's something serious. Please advise.