Perfect use but late on- pregnant?

Siân Melody🔮👻 • 22~ London~ Art & Politics postgrad student~ English Lit & Philosophy graduate ~ I’m a Slayer, ask me how ~
Hey guys so posting this because I am stressed out! 
Basically my last period ended on 17th May and I had condomless sex that night. That night was however my 2nd day back on my new pill pack which I had taken, I've continued the pack perfectly too. However I am now on my fourth of 7 day break from the pills which is my usual period start day and I'm still not on. Sometimes I do come on on the fifth day but this has happened rarely. 
I'm worried as I have seen a discharge in my knickers today instead of what should be blood. I have cramps and back pain but no period I'm so worried- any suggestions? Could I really be pregnant on perfect use of the pill? 😩