I've gone to concerts on my own, it's better than going with someone who isn't as into them as you are. I've done that too and it was miserable, I just wanted to dance, there was a gap we could have moved forward but she was just stood there watching and complaining about being squashed. I've been to at least 3 concerts without anyone and it's fine, if you get there early-ish to queue you can scout out some friendly looking people and go and introduce yourself. I made a great friend at a Katy Perry concert, still talk to her all the time and it was about 3 years ago now. If you think it's awkward introducing yourself just remember you have something in common! Best bet is look for someone wearing a band t-shirt, sit yourself near them then say something like 'Hey cool t-shirt, have you seen (insert band here) before?'
It's a lot more fun to be there on your own than with someone who's just going for the sake of it. The only problem you might have is if you queue early you have no one to wait for you while you go the loo but as long as you talk to someone they can let you back in.