4th baby???

Hi ladies, I currently have 3 kids one of which Is from my current partner. My youngest is 3, I know he would like 1 more. My question is has anyone else been in this situation? Did you have a forth or decide not to? I just don't know what to do. I'm constantly thinking about it, I often think I would like another but am scared. Scared of how much harder it may be. Any advice or past experience would be much appreciated. Thanks x