Think this is a breast attachment. This happened to me at 6 months. I tried co-sleeping, but baby wanted to suckle all night. Within a few days I was suffering from very severe sleep deprivation and so was my baby - she was getting less than ten hours sleep a day, instead of the fourteen she needs at that age. The day my baby slipped and bruised her face on the kitchen floor I knew I had to sort out the sleeping before between the two of us she suffered worse injury.
I went through "The No-Cry Sleep Solution" plan, made a lot of changes to LO's room to make it darker and quieter and made a very strict routine for the day.
Only then after I had put all that in place I did controlled crying.
My LO would go off to sleep, then wake every 45 minutes. The first night I did CC she went back to sleep quickly from 8.15 until midnight. At midnight I fed her but after that she couldn't get back to sleep by herself. I would leave for 5 minutes, go and shush shush for 2 minutes, leave for 5 minutes. Shush shush for 2, leave for 5.
I was sitting sobbing on the bedroom floor. DH was lying in bed begging me to go feed her. I just kept thinking of her little bruised face - I knew I could not carry on without sleep. After 2 hours of furious crying, shouting she started hiccuping. I fed her then and she went to sleep until 4.30, had a quick feed then back to sleep til 6.30. The next morning I rang the health visitor and cried down the phone to her. She said to stick it out for another 2 nights.
Night 2 LO went to sleep herself after 20 minutes, woke up again at 4.30.
Night 3 Lo went to sleep after 5 minutes Note I was still feeding her at about midnight and at about 4am.
I recommend "The No-Cry Sleep Solution for Toddlers and Pre-Schoolers" - she does suggest to use controlled crying but only as a very last resort on a breast attachment.