I honestly had the same exact problem with my now almost 9-month-old. She was sleeping through the night from about 4 to 6 months and then started teething and it ended for about one week and then she went back to it for about two weeks.
I thought perhaps it was a growth spurt, but I gave it a good month and one-half. Finally, I talked to my friend's aunt who is an infant specialist. She told me that she was at a touch point in the beginning, but then because I went in and fed her every time she woke she developed a habit. She said that after 6 months or a certain weight, there is no physical need for them to eat in the middle of the night. Because my daughter had always sort of done things on her own I thought she would go back to sleeping through the night by herself; however, she informed me that at this age she would not.
All that to say that in the end we had to do sleep training. I had "trained" my daughter that if she woke up I would come in and feed her so even though she had never done it before, now in order to go back to sleep she needed to nurse. It took us 3 nights of sleep training to get her to go back to sleeping through the night and she is much happier for it, as am I.
I promise you that it is going to be hard to do the sleep training, but it is worth it. We do not subscribe to the "cry-it-out" method, but instead did a progressive wait method, which allowed us to go into the room (the REAL Ferber method) and comfort her at different intervals. DO NOT PICK HER UP. This for me was the hardest part! It is difficult. God hardwired us as mother's to answer our babies cries and you still are (by going in for a moment or two and assuring you that you are there, but it is time to sleep), but you just can't pick her up. Everyone is different and everyone does different things that work for them and their family, so I would suggest to look into the different sleep training methods and choose the one that works best for you and one that you know you will be able to follow-through with and be consistent.
One other thing: My husband is the one who did the going in and comforting for the first few nights. We waited until the weekend so he didn't have to go to work the next day, but it helped because the second I would walk in the room she would get TICKED, because Mommy meant food. The Monday that my husband went back to work and he wasn't here during the day, she started testing me with naps. I had to do the same thing that he did. Go in, pat her tummy, talk sweetly and turn and leave the room. She was definitely beside herself when Mommy did the same thing and she realized that it was no different with me than it was with him. She did this for two naps and never did it again.