Hormonal Upheaval

So this is what's been bothering me lately a lot.
 Like most people who have kids or are planning to I want to be the best parent I can be. It's not like when you think about it anyone goes yeah I'm ok with just being an O.K. parent or I'm fine with not putting in the effort or time to make this little person the best they can be (or at least I hope people don't think that way). Normally most days I find it easy to be at my best but some days it is a struggle (we all have those days). That being said this pregnancy has played havoc on my hormones and I've not felt well most days. I was nauseous 24-7 for nearly 4 months and have been having hormone headaches almost daily since I got pregnant. Not feeling well and trying to parent at the same time is hard. It's manageable in small bursts like when you have a cold but this has been 5 months. Not feeling well and not sleeping well has made me extremely irritable which ends up causing me to snap at my kids.
Brandon seems to kinda understand that this is just something we have to get through but Danika and Lucas just don't get it. Don't get me wrong I am so thrilled to be pregnant again and can't wait to meet my new baby, but I am so ready for him to be born just so I can be me again. All of my other pregnancies have been symptom free so they were easy to go through this one I feel like invasions of the body snatchers has happened lol and I just want my body back! ;-)
I feel so bad for the way I treat my family lately but it doesn't seem to be under my control. I try really hard to not get frustrated or angry at the little things but everything just irks me. Parenting has been a strange balancing act for me lately. It's been me snapping at my children followed by me trying to show them I love them. It's like I'm constantly trying to play catch up. All the while trying to make them all 3 still feel as important as the new baby is.
I really am trying to keep things even I always have between the 3 kids trying to not treat the oldest different than the youngest but treat them what's appropriate for their age and keeping the same rules for them all. I know once the baby is born that they might feel, I don't know, replaced but I'm trying my hardest to make it not that way. We are going to make an huge effort to still get one on one time with each kid so no one gets lost in the shuffle!
I just wish it didn't seem most days to be such a struggle to get through but I do know it wont always be this way and I will get back to being the fun loving strictish parent I used to be :-) not the grumpy old lady who crawls out her cave to growl at everyone every day!