my period usually hits the 13-14, and stays 2 days. well last month it hit on the 17 but was one day and just spotting. this month it's just gone. no symptoms of it coming soon either. my boobs are sore, and my nipples seem darker. I feel nauseous and stuff as well. I've taken 2 tests on two separate days, both at night. and both looked like this, which is obviously negative. what do I do?