Feeling so alone and empty?

For a while now I've been feeling so alone and empty. Let me explain.

I am naturally a shy person and lack confidence but I do also have times where I am sociable, go out with friends and family, talk to pepople etc.

But then out of nowhere I become dead quiet and I don't know what comes over me. I become very unmotivated, nothing will excite me and I feel very lonely and empty. I will isolate myself and just cry and hurt.

I am often alone all day and when people come home o want nothing to do with them?

I feel like I have no one to talk to about I feel, I have close friendships but I feel like I am hogging them down or annoying them when I talk about my feelings. I, Close with my mum and she always says I can talk to her but I don't feel like I can.

All my college friends live so far away so I don't really meet up with them outside of college and I have had no motivation to talk to or meet them.

I'm learning to drive too and I just feeel like a idiotic failure all the time.

Any advice? I'm 17 by the way