hate to say it, but this is normal baby behavior.
crying it out doesnt work, because it doesnt. www.askdrsears.com has some info on crying it out sensibly, and its usually not until your instincts tell you that your child doesnt need something immediatly. usually doesnt happen until around a year old.
the lack of sleeping can be caused by the teething. also, simple developmental things like rolling over, crawling, etc will all cause sleep disruptions.
babies have tiny tummies. they have to eat when they are hungry. if thats what it takes to get him back to sleep, dont feel that for any reason you have to deny him this. it is a myth, and a LIE that children this age cry for attention or to manipulate us. they cry for a NEED. thats the only reason babies under a year cry. trust yourself and trust your child to tell you what he needs when he cries! listen to it! :D you are the only one who is the expert on your child.
take a break from working if you can. i also run an in home child care, and i know what its like. i only had 2 kids at the time my son was that age, and we just made due. we coslept because that was the only arrangement that would allow us to sleep. it might be easier that i was breastfeeding, breastfeeding while bedsharing made it easy for me to get more sleep... you dont say either way what you are doing, so its hard to say. obviously a bottle requires preparation at some point, but read on...
you can prepare bottles before bed, and share with hubby. you do one, he does one. i do believe it is safe to leave a bottle of formula out in room temp for 24 hrs, so overnight would be fine. just stay in bed, have baby in the room with you if thats possible to reduce the amount of running around you have to do at night. its best if you can stay in bed and get baby back to sleep after a feeding if he's right there next to you.
during the day, a lot of sling time will help. the moby wrap is the single most comfortable sling i have tried. its extremely helpful! you will also be able to use it with any future child care babies, so its WELL worth you purchasing it! just have patience, as you know, this time doesnt last long.
tylenol is perfectly safe for infants, if the dosage isnt on the bottle, ask your doctor, or www.askdrsears.com might have that information. i know 'the baby book' by william sears has a chart that specifies tylenol amounts by weight which is awesome.
anyway, good luck.
as you know from having 2 other kids, sleep is never a constant, once you get into a rhythm something changes and someone isnt sleeping again. trusting that YOU know better than anyone else will be the key to happy parenting. only YOU know your son and have the tools you need to specifically care for him. trust yourself!