Is it normal to go in and out of depression...?

ok so my story is kind of long so bear with me. Im 18 and just got done with high school this past june. Ive only just started to date and i was with my first gf back in december needless to say we didnt last long only 7 weeks but she was and is still my best friend. Then like another 2 months went buy and i started to go out with my second gf this to also lasted 7 weeks and we broke up like the middle of april and since then i havent gone out with anyone else. now im not a shallow guy i dnt care what anyone looks like because i dnt rlly find anyone attractive(is that normal?) but i had stuff in common with them. now me and my second ex dnt tlk anymore or anything which im fine with i dnt wana see her anyway but thats besides the point. now since my ex broke up with me ive bin having a feeling of depression occuring randomly lasting for a few days to like few weeks. my friends know this about me and some dnt complain to me about their relationship problems but the few that do tosses me deeper into my depression if im depressed also when i see others with whom ever they are with hurts. now what i liked most about my last ex is that i wasnt alone and had someone but once it ended im not one to cling to something. now since then i havnt found anyone i would want to ask out cause i dnt see a spark there and that gets to me. so now im feeling like im so freaking strange because of thoes reason so if anyone has anything that might help then please do tell me.