Hello to everybody im new to this site and i could use some advice from other stepparent.

A little about my story me and my husband got custody of his now 5yr old daughter but the las time we saw her she was 4 months old. Once the babymomma knew me and her ex where going out she took off and never heard from them again, now 5 yrs later we get papers to go to court because babymomma is in trouble and someone needs to take care of her kids. My husband thought about signing his rights over but I told him not to do it that we could take custody of her. So we did but I never thought I would feel the way I feel now. Since the babymomma took off 5 yrs ago me amd my husband had a little boy he is now 3. Babymomma was always causing problems even thought my husband and her were over and lets just say she is one of my least favorite persons in this world. But anyway lets just say I havent been happy since my stepdaughter is here I know she is just a little girl but I feel like she knows what shes doing and does it to get it her way. I take care of the kids during the day and when im here she listens to me and behaves but when husband gets home she starts acting like a 3 yr old and stop listening to me and talking to me. I dont know if all 5 yr olds are like this but it really gets me mad and frustrated. Ive told my husband about it and he says its just me seeing thing and that im being territorial. Im not a bad person everybody that knows me knows im always trying to help out others even though sometimes nobody helps me. The husband and I have been getting into arguments everytime I tell him something about her or when I try to tell him how I feel. Im only 25 yrs old and I dont want to be unhappy for the rest of my life. I was just use to only being 3 of us and now that she is here I feel like she is taking mine and my sons place. Im so confused on why I feel unhappy since she got here. I need advice or even maybe hearing someones elses story might help me out. Like I said before im not a bad person and I want to be happy again but I dont know how to take this sudden change in mine and my son life because the husband seems to be worry free and I want to be like that again. Thank you for reading and any opinions are welcome, thanks once again.