5 months is around the time my daughter (now 10 months old) stopped sleeping through the night. We only recently got her sleep to a point that is comfortable for the whole family.
It is certainly possible that he has a cold or something, but it is also possible he is just entering the next phase of development. Many books say the night waking and crying is related to the becoming more social and aware and wanting to be with you whenever he is awake. The books also say that we all wake up a little between sleep cycles and your baby simply doesn't yet know how to get back to sleep on his own.
In my home, we tried white noise, music, snugglies that smell like me, dark room, light room and other tricks, but really it was my husband's and my behavior that dictated how she returned to sleep.
As with all things parenting are plenty of different approaches to helping your family stay comfortable and rested and I they are not necessarily as black and white as 'cry it out' vs 'attachment parenting.' For not crying at all, we tried the book, the 'No Cry Sleep Solution' and read some Dr Sears - these just didn't work for us. We tried me sleeping in there with the baby, but I was uncomfortable and the baby and I were both up constantly. For a couple months it worked for me to have just two times a night I'd go to feed her, any other times she woke up, my husband would soothe her and yes there was some crying (we got this from Healthy Sleep Habits, Happy child).
I can tell you how we finally ditched the night wakings, but it involves some crying (took 3 nights, never crying more than 5-15 minutes, gentle soothing...), but maybe someone else can describe success with no crying.
Good luck and good sleep to you :)