I've been sick with strep throat i am now better but i can't sleep at night so i took nyquil. but then i slept all day. now i can't sleep what can i do?

Re-establish routine: Sometimes after you have been sick, it takes a little time to get your sleep cycles back on track. Try gearing down about 2 hours before you want to fall asleep and avoid use of led emitting electronics for those 2 hours as well. The light emitted form these can reduce your natural melatonin, a hormone that helps with sleep. Warm milk, a good book, a relaxing massage, warm bath all can help.

The hangover: Sedating antihistamines like that found in nyquil have a lot of residual side effects, namely sleepiness and dry mouth, that last through the next day. Don't worry, pay less attention to the time. Read or do other relaxing activities and make sure you wake up at normal time on a night that you can't sleep. If you keep it up and sleep later every day, you will have insomnia that hangs on.

Regular schedule: Good sleep hygiene is important. Part is going to sleep and waking at a consistent time, avoiding sleep medications or sedatives such as the antihistamines in otc meds. You might consider melatonin to help restore the sleep cycle which is normally used by the brain for this reason. If you still have problems see sleep specialist.