First, repeat to yourself several times a day that you are a good mother, a loving mother, and that you love your children, even if they drive you nuts.
Second, if your 15 month old is waking up crying and in a rotten mood, ask your pediatrician to please evaluate him for everything - are his ear tubes ok, does he have acid reflux (my child's problem-lie down and have acid eating at your esophogeal tube and see if you feel happy when you wake up! NO!), does he have allergies, is he eating or drinking too much before he falls asleep or what? If he has none of these problems, realize that there are children who are sometimes out of synch, that which the rest of us feel restorative is very unnerving to them. There is a book called The Out of Synch Child, which is very good about helping parents identify areas that may be adversely affecting our children because we don't realize it is a sensory overload for them, and there is also a book called Children with Starving Minds, by Jacqueline McCandless that is also good. At one time, I couldn't go into Walmart or HEB or Costco without my son screeching constantly, people thought I was kidnapping him or torturing him. Leaving and coming back didn't make a difference because the sensory overload from the large loud environment was too much for his nervous system to handle.
Lastly, you may want to ask your physician for a referral to have your son evaluated for developmental status. If his environment is too much for him, a good physical therapist or occupational therapist can help him overcome his sensitivity. It is so hard to figure out if your child's behavior is out of whack with every other child of similar age because we get used to so much and we moms are very good at accommodating our children. I suggest the evaluation only to make sure there is not something going on that is beyond our abilities as moms to handle. If he is fine and the evaluating developmental specialist says there's nothing out of synch with your child, be very thankful, and keep him very very busy. Get a swingset, get a swing, get him in it. Get toys that help him move and keep him active. The more physical activity boys get, the more grounded they are and happier they are and more able to deal with the things that don't bother most other children.
Good luck, and no matter what, remember, you are a good mother!