8 month old just started crying non stop about a week ago....

He may be going through a phase of separation anxiety. It's normal and babies/toddlers go through a few of these phases as they grow up. Give him as much attention as you can during the day and sit next to his crib while he falls asleep. Also, don't rule out teething. It's a long process and he could be starting on his molars, which are very painful. They start growing well under the gum so even if you can't see them, they're still there. Try giving him some teething tablets. They're homeopathic (no drugs/medications involved) and they generally have four remedies in them, one of which works on sleepless and grumpiness.