Lack of motivation usually is the result of taking the road less traveled by, doing stuff you don't like
Facebook? I thought no one uses this anymore, I've left Facebook since 2008, if you gonna study hard you need a less social life for the studying period at least, otherwise go for easy stuff
We aren't born with abilities to control our emotions and feelings, but with practice we gain such abilities that leads to success in life, just as the way we aren't born educated but we educate our selves
So it's better to stick to what you got and to stop wasting time changing the field of study