I miss my "old Life" :/?

I'm only 15 but i kind of miss what my life was like months ago, mainly back in summer. I get like this sometimes but its only usualy for a short while and it gets better but this time it hasnt. Im getting really depressed recently, since October began. I did so much in the summer, it was probably one of the best times of my life, i made friends with people i had before been enemies with, went on an amazing school trip to Germany, my mild acne that bothers me so much cleared up for like 6 months !, i had a period were i dated alot of boys, i was really close to my friends, we went to these amazing gig's. I had a great roadtrip with my family around france for a month, the weather was fantastic all the time, i was always outside, an we all went to loads of camping parties. Now, life feels sutch a drag! Its snowy, cold, school works got so much harder, i've stopped talking to most people and it feels like some of the people i once loved have forgotton about me. I feel really bad looking and just fed up :/ Everything seems to of changed and theres nothing to look forward to. I just miss all of that so much and want to go back ! what do i do to feel better about all this ?