Had Protected Sex. No Signs Of Pregnancy. But Light Brown Discharge. Normal?

Hello i need some help. My periods are usually 30 days apart but for the past 2 months they came on early. On June it came on a day earlier on the 23rd 2012 then in July it came on the 19th. My period are usually 4 weeks apart. I have a 6-7 days period. On the 28th of July me and my boyfriend had protected sex. On August 14 i masturbated at 1am and i started to spot very light brown for a whole day when i calculated my period is due on the 16th. It s the 15th now and still no period. I am alittle stressed now, i am having some pms symptoms, my face is breaking out and my breasts are alittle sore, no cramps , slight headache . By the way i started taking iron pills for this month. Is this normal for me? Help please...