D.P.
I think you have gotten some really good advice so far. Life sucks sometimes. Sometimes it sucks a LOT, and for a LONG time.
I think it's good advice top find someone, or a few people or a group of people with whom you can be totally honest and reveal you innermost thoughts and feelings. People that can relate on some level to what you're feeling.
Also, I don't think you need to "put on a happy face" to the world at all times.
Therapy might help, as well.
I'm not sure the gravity of the medical issue you are dealing with but I would certainly keep seeking, asking, trying, etc (like it sounds like you have been). If it were my child, I, like you, would not be willing to yell uncle until the last glimmer of hope was extinguished and there is always hope, new medications, procedures, etc. to look into.
Plus sometimes I need to be reminded that prayer is often answered in an less specific way than we think it will be. God doesn't answer prayers in OUR way, but in HIS way. We can't see down the road, but He can. Sometimes it seems He has closed every door, but what He's really doing is opening another, more perfect door.
And sometimes keep in mind that when our prayers aren't answered as we would like it might be to save other tragedy, heartache, physical setbacks down the road.
I wish you strength and guidance and wisdom for your life. Take it day by day. God bless.