Uterus/belly shifting at night?

Ann Marie • 35, Boston area. I have a 2-year-old son, pregnant with my second, due July 2018
I'm 14w today. No bump yet, but things are starting to shift... For the last few days, during the day, I feel my uterus low in my abdomen, right above the pubic bone. I go to bed, and when I wake up in the morning, I swear I can feel my uterus much higher, just below my belly button. By the time I get up and shower, it's back down low, hidden in my belly. Have you experienced this? Does this mean I'm about to pop? It's driving me crazy bc every day, I think "this is the day my bump finally shows..."