First of all, I would think part of your feeling bad would be your hormones readjusting. Because you just stopped breastfeeding, they're still wonky.
As far as your son sleeping, you need to get him on a sleep routine. It may take a few nights, but it will work.
1. Make sure he's resting enough during the day and that bedtime is at a reasonable hour. Babies who are overtired are harder to get to sleep.
2. Get a routine. We do bathtime, put on pjs, brush teeth, read a book, and go to bed (my son is 19 months).
3. Put him in his crib. I wouldn't leave too much light on. I don't use any with my son other than the light from the clock/sound machine. I also use a sound machine and have every night since my son started sleeping in his own room at 7 weeks.
4. If he will not settle down, don't rush back in immediately. Give it 10 minutes or so. Never let him cry more than 20 minutes before checking on him, though.
5. When you go in to soothe him, don't pick him up. Just pat his back or stroke his hair and say "It's time to go night-night/sleep/bed."
The only time I pick my son up if he cries at night(which is rare) is if he suddenly wakes up screaming, which is usually a sign he's had a nightmare or is sick.
Stick with your routine. You will have some long nights to start with, but I think you'll be rewarded with more sleep if you stay the course.