Could I be pregnant please help I'm young.

First day of last period was July 28th! My cycles are usually 30-35 days! I had sex on the 8th & 20th of aug. (Unprotected) I had a wierd mucus of blood in my underwear sorry tmi on around August 29! I have really sore boobs and brown rings aroun my nipples with a lot of bumps! I'm really tired too. A lot of cm mucus but non period I took a hpt last weekend and it was negative. Could I just be too early to not have enough hormones in my system?