[Pregnant with # 3!]

After having my 2nd daughter -18 months ago- I put in my 2 weeks at work. But after getting a guilt trip, I agreed to work 1 day a week, & help out w/ as much as I could get done. Even w/ working just the 1 day, I can't get away from the stress that goes along with it.
So I sat down w/ my husband -who has wanted me to quit this job all together- & decided that I have to quit again, but this time go all the way w/ it. I tend to be a people pleaser, so it is going to be hard, but when I go in this week I am handing in my keys, collecting all of my pictures and nic-naks, and getting out of there for good!

My question is, would it be okay if I write my boss a letter to tell him how I feel, and ultimately quit? I think it would be easier on me, and it would allow me to get it all out there, because I know the situation will make me very nervous, and hence forgetful.
A little about me: Wife to wonderful Husband, Mother of 2 beautiful girls (3 & 18mo) & 18 weeks pregnant w/ baby 3! I go to school FT working towards a Dental Hygiene degree, & (as a favor to my boss) I continue to work PT as a Dental Assistant. Amongst everything I take on, my Husband works FT & we rearrange our schedules so that one of us is always home w/ our children.