I hate the feeling of loneliness...?

It's summer, and I have friends. It's not like I don't have those days where I hang out with friends or have a sleepover, just sometimes I have a day(s) where I have nothing to do. So I'm mopping around the house in my pj's with no make up on and feel lousy. Some of my friends only have 2-3 days of boredom through their whole summer, which those friends are popular and outgoing. Unfortunately I'm not THAT popular or outgoing, but they always have something to do, which leaves me feeling useless. How can I get rid of the discreet feeling in the pit of my stomach? Help will be very much appreciated.