D.D.
I think there are times when it's good to reflect on where you are and where you want to be. Instead of questioning everything and coming to the conclusion that none of it is good enough how about writing a list of everything that's great in your life right now. Then a list of stuff that could be better with an action plan of what you need to do to move it into the great list. And finally a list of crappy stuff and what you need to do to move it into the could be better or great list.
I'm over 50 and I gotta tell ya that it's great. In my 20's and 30's I was so busy raising little kids and in my 40's I was working like a dog to make sure those little kids who transformed overnight into teens had what they needed to succeed in life. Now in my 50's I can sit back a bit. I no longer have to keep up with any trends or feel the need to wear anything other than comfortable shoes. I have time for my hubby, pets, kids, and grandkids.
So go easy on yourself as you turn 40. It's a tough decade of birthdays but it'll get better.