I use microgynon.
Last month, I didn't take my break as I was on holiday so started my next pack immediately. I am due to start my break today. However, I will come on on Monday and have a period for a week solid. I am going to London next weekend and it'll involve lots of walking etc and I don't really want the inconvenience of having to find loos for changing etc.
Will there be any adverse effects if I have a third packet?