Michelle, I have not read your other posts or threads, but I do feel for you and know what you're going through. I can offer some things that worked for us, I would guess you've heard most of it before.
I'm a first time mom to a 10 month old. The first 3 months were VERY difficult. It was hard to see the light at the end of the tunnel. But, it IS there. Hang in and know what a good job you are doing.
-Can you any of your friends offer help or support? There is no shame in asking for help. It's a tough, tough job....especially with a lack of sleep.
-Have you tried a co-sleeper? We used this from the beginning and it was a blessing. She was literally right next to me, but in her own space. I think this made the transition to her crib much easier.
-Yes, entertaining a 3 month old is weird. She seemed to like to watch things above her head, as she lay. I had one of those gyms with the criss/cross thing and stuff attached. She would look at the things for a few minutes...just a enough time to shower
Does he like a stroller? We have walked the local mall hundreds of times. The change of scenery seems to be KEY!!
-There will be fun times....amazing times, scary times, crazy etc...it's a journey. I've really had to work on living in the moment. Before baby, I had everything on a schedule, planned and neat. Now, the house is trashed, schedules are out the window and I live for each hour. Try to enjoy and think of the positive side of things. It sounds trite and cliche', but I really think it's true. Many, many things in life are a choice...how we look at a situation.
-Do you have a plan for returning to work? That is going to be a very big challenge for sure. Is there anyway you could go part-time...
-Boo on your DH...even though he's working too, he needs to find some way to help you. You're working 20 hour days with no lunches, breaks. Can you have a calm, honest discussion with him? If he want you happy, he should be willing to provide some help.
-You are not a bad mother. You're a new mother. Think about it this way. What other profession do you know, where the worker becomes an expert in 3 months? Imagine a pilot...they go to school for years, practice for thousands of hours before they can fly other people anywhere. (Weird example, it just popped in my head!!) Yet, mamas expect themselves to be "perfect" after a few weeks of this most important job. BTW...no such thing a perfect.
-It sounds to me like you might want to consider the MIL...I know, know, I'm right there with you. But, if I were truly "at the end of my rope" I would accept help from just about anyone. Be humble, see what you can learn. USE her and get some rest...go out...relax.
Finally, do your best not to compare yourself to others. YOU are doing YOUR best. That's all you can ask of yourself or anyone else.
Thinking of you,