Hi Bernie,
At three months of age, he's still a little young to expect that he can self soothe. Most babies don't gain the ability to self soothe until between 4 and 6 months of age. And since he has reflux, then it's not surprising that he also has troubles with sleeping.
Have you tried swaddling? If he likes the sling, he may do well being tightly swaddled. The Miracle Blanket is something many parents like for swaddling, which you can find here:
http://www.miracleblanket.com/
If he prefers movement to sleep, then perhaps a swing or a bouncy chair might work for him right now. Then, again, as he gets older, you can transition to working on teaching how to sleep without the props.
Also, at this age, it's okay to rock or feed him to sleep and then work on teaching him to sleep without those props when he's more able to self soothe.
Did he doctor suggest that you try angling his mattress to help with the reflux? That might also be worth a try.
Since he's still young and with the reflux, then there's a good chance crying it out most likely won't work well for him.
Keep us posted on how it's going and what you've already tried. We can keep working on finding something that helps at least get you all some rest.