One of my friends sent me bitcoin so I could buy something online. They used the website quickbt to send me the money. They used the proper address for my wallet because it was copied and pasted in. That was three days ago and I still haven't received the bit coin. The wallet I'm using is bitcoin-core, and whenever I open it on my laptop there's a loading bar at the bottom of the window that says synchronizing to network (it's been doing that for three days as well). I was wondering if anybody could help me or if anyone has had this problem before?