Mental health problems or just sad?

So, generally I'm quite not happy but just okay with everything, sometimes I have really good days however, I can flip in seconds, I won't necessarily get angry but agitated by everyone and snap at people, it has ruined a lot of friendships and I generally feel like being alone and chilling in my room, but I also have times very rarely but common enough, where I just feel alone, no matter what situation I'm in, it just doesn't register that there's people near me, like I zone out and all I can focus on is a dream in my head where I'm a little girl walking down a country lane with masses of flower fields either and an occasionl car going past and just driving no past me with no acknowledgement. The agitated emotion has been happening for 3/4 years where as the alone has been happening since I was about 7/8, I'm now 15. I know none of you can diagnosis me or anything but was just curious as to if anyone had similar things to me or if there was a name for it. 
Thanks for reading.