Placenta

So yesterday i folded my threadmill and it was really heavy and after that i got this cramp but it went away and the next day i hardly felt my baby move though she is moving shes bearly kicking and im scared cus that threamill was pretty heavy but the next day i was having pain in my stomach when i sit down it hurts but idk if thats from sitting all day but idk how to describe the pain but it felt more like stinging then pain and again idk how to describe where the pain was but it was under my breast on my rib cage but in my stomach part but now is that something to worry about? Im a ftm so maybe my placenta ripped? Should i go to er? Is that normal?? Im 34 weeks btw