Help! I am new to sewing and have already caught the addiction bug! All I want to do is sew, but I keep running into major road bumps!!

I measure a size 14 on the back of a pattern.
Bust 36
Waist 29
Hips 40
I wear a size 4-6 in real life. I construct a size 14 garment and it fits like a size 10 in real life. Way too big!

I look at the constructed garment wear and ease and it looks like I should do a size 6-8.
How can I be somewhat sure I am going to get a garment to fit me once constructed? Muslin I can do no problem. But what pattern size do I start at?

Also if the garment is 2 inches too big, how many sizes is that? Meaning, is there a 1/2 an inch between each size?