What's going on?

So ladies! Hope your all having a grand day. Right, I've missed mg period for 21 days now, no sign of aunt flow showing up however, I'm getting a lot of mood swings, a very short temper and lower back, belly and hip pain. Some smells make me feel really sick, I keep getting horrible headaches, I'm constantly tired and to top it off I look rather bloated. I've taken 3 pregnancy tests and 2 have came back negative while the last came back invalid... could they have been faulse negatives? Could I actually be pregnant? What's going on...