Edit: Wow this was longer than I thought. Sorry for the Paragraph xP Well I'm singing in a church for fun (I've only had a few lessons.) But one thing is still evading me. I can sing GREAT! when i'm singing along to someone else who is on key and sounds great such as listening to like Beyonce or Sam Smith on the radio but if I turn the music off I can't tell if I'm on key or not. Also if someone sings with me it throws me off because for some reason I can't sing by myself I have to match the person its almost subconscious. Like all four of us are singing. The key of the song is too low and I am awkwardly going between singing it low but (I can't sing low and loud) and singing the key high to match everyone. I am slowly getting somewhat better about this but harmonizing is still difficult. I can't listen to someone sing and just harmonize right off of them like other people can, because like I said, I have to sing along to them. Also, they cant harmonize to me because if I am singing low, and they start singing a higher key I naturally move up in the same key as them. I can't stop it either. I can somewhat alleviate it by covering my ear or ears and singing but it isn't sustainable. Any help would be greatly appreciated.
For starters, apart from the ubiquitous 'get yourself a teacher', sing along with tracks that are within your range, and gradually, over a number of sessions, keep turning the sound down, until it's barely audible. Then some more, but only for short periods - maybe start with a couple of lines, then increase, so when the music comes back, you'll tell if you're still in pitch. It may take several weeks or months, but it's worth a go. It'll also check your timing - but for now, tap a foot, sway, or whatever you like to keep in time.
It sounds like your range needs a little work, too, so keep singing those low and high notes more and more. Being an octave out isn't a problem, and as long as you're aware of it, it's a good sign.
Can't tell from the phrasing of your question whether you had lessons previously, or you've just started, so only had a few, but your teacher will be able to help with this. Also, trying to play an instrument will help differentiate pitches.Say, on piano/guitar, you play C-E-G-A, and sing it back, with or without playing again, then increase the notes, and try again. Try to record all that you do, as a reference to improvement, as well as listening to what you're doing. Quality of reproduction isn't foremost, yet, so any old recorder will do. Chances are your phone will do a fair job.
I think you should practice ear training and establishing a key in your mind. Practicing some scales and arpeggios will go a long way to helping you establish a sense of key. Practice them using solfege or letter names or numbers. Play a note and then practice going up and down and returning to the same note you played. Once you have scales try arpeggios. The Do Re Mi song from Sound of Music is a great example of solfege. Try singing each part while thinking the starting note in your head.