OK, so... this is a really common thing that happens when babies move into their own room before fully sleeping through, and parents are (understandably) knackered after many months of broken sleep.
The problem arises because following the path of least resistance involves breastfeeding baby lying down in your bed, so that you can get more sleep. Completely understandable, but by baby not going to sleep in the cot then you create these unwanted sleep associations (ie baby wants to cosleep upon waking). In the longer term this could well end up with baby getting in your bed earlier and earlier and wanting more and mpore comfort feeds.
IT's going to be hard work to break this cosleeping sleep association, but if you want baby sleeping all night in the cot then the longer you go without dealing with it, the harder the habit will be to break.
So solving this, the Number 1 thing to do is consider where the cot is going to live, while you teach baby to sleep through and night wean. Thing about this with your logical and practical head on, not your wishful thinking head on.
It's going to be hard work, youre going to be spending extended amounts of time hanging over the side of the cot getting baby to settle to sleep in there.
So, will you go for the path of least resistance? I did when my children were this age, especially since I have 4 children to consider. The path of least resistance is to do the sleep training with the cot back in your room
(for anyone reading this, I would always recommend keeping baby in the full sized cot in the parental bedroom until consistently sleeping through. If you don't you often end up cosleeping by the backdoor, when you never intended to)
You can do this with the cot in the nursery if you are OK with that. But bear in mind that this wont be solved fully by the time you're back at work and so you will be very, very knackered having to get out of your own bed to deal with baby.
To settle baby, at this age it involves basically being very consistent and keep repeating the same thing over and over again. Keep your tone calm and compassionate, dont lose your cool and get annoyed (even at 3am after 90 minutes next to the cot!)
I'd stay with baby to do the settling. If baby can lie down independently then keep on telling baby to lie down if they stand, or lie baby down if he cant do it himself. Firm hand on the chest to keep him still and reassured. Use your sleep prop to encourage self-settling - so a dummy and/or comforter. Keep your voice low and quiet, nothing stimulating, keep baby lying down and reassurance until quiet.
Stay next to the cot repeating the same thing over until baby is quiet. Once quiet do not make a move to leave (even if it's 3.30am and youre exhausted). Stay reassuring with your hand, stay still without any stimulation and wait. Wait until asleep and then wait another 5-10 minutes after baby is asleep. Then remove your hand from baby's chest and go back to bed yourself.
If baby's cot is next to your bed, this can be done while you are lying in your own bed. If you have short arms (like me!) and have spare cash, a dropside cot makes reaching down to the cot mattress easier while lying in your bed.
Follow the same routines at bedtime and naptime for consistency. Night weaning will probably help and seperating feeding and sleeping and bedtime and naptime.