The reason I asked so many questions is because I went through a similar thing a couple of years into my relationship with my husband.
I did as MitchellGirl suggested to you and went to my GP. He had been my family GP for years so I could just go in and chat to him. To cut a long story short I realised that I was incredibly unhappy with the way my life was going. I was doing a job I hated, I was lonely (my job involved lots of time working alone), the job was demanding so I barely had any time to see friends and family. I felt my life was miserable, I felt powerless, like I was observing life but not really taking part.
On paper I had a fabulous life - I had the great job, responsibility, a wonderful boyfriend, a lovely home, no money worries. So why the feeling of melancholy all the time?
I started the process of getting back my mojo by, first, being very honest with my boyfriend. He was incredibly understanding and supportive. I did turn it round with his and my GP's help (new career, new hobbies, properly switching off after work, date nights). A two year process in all and I haven't looked back since.
That's (the short version of) my story boole, but I cannot help but think you may benefit from hearing it. The first step would be to speak to your boyfriend about this. Be really honest and tell him you are picking on him without cause. Do apologise. He may appreciate that you recognise there is a problem. You never know, he may help you try and get answers as to why you are being the way you are.