Do you think you could be depressed? Low self esteem is a symptom of it. I have felt exactly the way you describe, and still do most of the time. I know it sounds a bit patronising, but do you go to any M & T groups, or get out and meet new people? I have made some friends at M & T group, and one I see fairly regularly. There are three who go together, who I really like, and am considering asking for a girls' night out. This time last year, I was LONELY, and thought that I would never make any new friends. The two that I did see were 'once a month' friends. I used to drive places in my car just to get out of the house.
Now I am busy nearly every day. I have a job finding time to do the shopping! Even if it is a coffee in town, or a quick visit to the zoo, you need to get out of the house. Start talking to other mums that you see in shops with children, even if you only ask the age of their child. It gives you a lift to have an interactive chat with someone.
I am sure that your dh loves you. If his mum is coming to stay, ask her to have your ds for the day, and book a pamper at the local salon. Or, meet a friend for a gossip. Or, buy a cheap book, and read it in the bath for two hours. You get my drift. If sge is there, make use of her.
Are you totally sure that your friendships are over? If not, try ringing them, and tell them how you have been feeling. Make an effort with them, and they might return the compliment. The trouble with feeling the way you do is that you become self-absorbed. I am not having a dig, as I have been there. Everything was happening to me, and I was so hard done by!
Finally, 15 months of not sleeping is enough to make anyone miserable. I had eight months of it, and was a wreck, so I can totally sympathise with you. Perhaps you could book a night away in the local Travel Inn while your MIL is here, and have a good night's sleep? It is really not a bad idea!