14 weeks pregnant and my kids stress me out

I have a one year old and three year old and they just always fight or there just always naughty I find I’m just constantly yelling at them I always leave smacking out of it as much as I can but I’m just worried as I’m pregnant and just don’t want to stress as I have had miscarriages before. I work three days a week so I do get some sort of a break but when I’m not working they are with me and I feel they play up more for me when the dad isn’t around :( today I actually had to lock myself in my room for 5 mins to calm the fuck down I shouldn’t have to feel I need to do that :( any tips please?