How to ask to work from home

So, for the longest, I have been meaning to ask to work from home. Here's why. When I was interviewed for my position, I was told that six months into my job, I could work from home - full time. Trust me, I was excited beyond belief and gave my all to this job. I even told my husband to give me the room I needed to do 'extra' on the job because I wanted to prove that I was worth it. Anyway, being the efiko that I am, I didn't ask to work from home until a year into the job. Not only did I wait a whole year to ask, but I asked to work from home just one day a week. Don't ask me why. It must be a Naija thing - I didn't want to do aseju or appear overeager. I didn't want to jump at the earliest opportunity. Like mention it at my six-month review or something.

I waited a whole year to ask. You guessed it. I was refused. Soit disant that things had changed, the mood on our team was no longer the same because half of my group had been phased out. The work from home thing had been kinda sorta cancelled but I was told that if I had a business reason to work from home, I could. Now, what's a good business reason to work from home? Anyway, over time, this 'rule' has changed to "You can work from home whenever you feel like, just let me know". I take advantage of this from time to time. However, it's been a while since the other half of our team was phased out and I am thinking of asking to work from home again. This time though, I want what I was promised at my interview. I want to work from home full-time.

What are good reasons for asking for this besides the fact that I was promised this at the time of hire? I am going to speak to my boss tomorrow (for sure). I say this all the time but I mean it, I will definitely bring it up tomorrow. However, before our meeting, I want to be prepared. Anyone that can help, please do. My biggest reason for wanting to do this now is because I am preparing to have a baby and it breaks my heart to have to leave my child with people I do not know. That, and the fact that I haven't found a daycare - all the ones I called have a sixteen month waiting list. I don't think this would sit well with my boss but it's the truth. What's a girl to do? I am willing to look for another job if it doesn't go well. I just need to know now so that I can start looking. Again, it's quality of life over anything else.