Q: Every Time i connect my MacBook pro to my iPhone hotspot it connects for a few seconds then drops

HEllo, so a week or so ago i had my MacBook formated and now it's running on yosemite 10.10.2 and I've noticed some problems with the wifi, I've searched about the problem and it appears alot of people are gaving the same problem and i tried to erase the wifi plist and that helped with the connection to my house router. But when I connect my MacBook pro to my iPhone 4G hotspot it connects for a few seconds and then drops and says there is no internet connection although it is connected? i don't know what to do and how to fix the problem? And i'm connecting to my iphone because it's alot faster. Another thing is sometimes it connects and it's perfect but mostly it keeps dropping every two seconds