I'm sorry, I don't feel that certain points in the posts above are accurate advice.
Is baby BF? sounds like he might not be getting enough to satisfy him
I disagree with this. If the OP is breastfeeding, by 5 months, her supply would be absolutely fine as long as baby is putting on weight steadily and having plenty of dirty nappies. There is no evidence from the OP that there is something wrong with her milk (that is if she is feeding), the baby is just waking every 2 hours.
Feeding every 2 hours can be very normal for babies, sometimes up to 10 months and longer. It isn't what you want to head, but it is normal for a lot of babies, yet, in our western society we continue to look for 'solutions' to solve alleged sleep 'problems'. This 2 hour thing is common for ff and bf babies too.
Babies triple their size within about 2 years, this requires calories, and lots of them. There is fewer calories in cereal than there is in formula or breast milk. Milk is more important to babies for the first 6 months, when solids can introduced.
Waking ever 2 hours could be for a number of reasons and not just about milk - teething, growth spurts, development changes, too cold, too hot, wants comfort - the list is endless.
I'm sorry your knackered OP, perhaps get rest in the day, nap with baby, or get someone to watch baby whilst you sleep.