My heart is aching what would you do?

I have just found out that I am pregnant with my 5th child. I had three of my own then met my partner 6 yrs ago and we have a daughter together who is 2 1/2. We had a quicky randomly last month and didn't use protection. I'm 36 an do know it only takes one time and we blew it. I am so unsure of what to do as we have a house that is full and four beautiful children already who we try to give the world. We are already stretched attending all the sports and feel life is full and didn't plan on anymore. Atleast not while we live here. I have had abortions in the past at times when a child would have been too much but this is no easy choice as I feel this would be my last baby and saying no would mean no forever because I wouldn't abort now to have another baby next year for example. I don't believe that's the right way to go about things. If we had a large home there would be room. I have joked about not being done and in my heart I love being a mum more than life so I'm so torn. Each of my children is so unique and special and I don't know how they would feel either I just feel so lost and scared. I haven't told my mum as she will be more negative than positive and I have no friends at all to talk to. I'm so alone right now with this huge choice weighing on me and it's so heavy I can't stop the tears rolling. I don't know why I'm asking other than what would U do ? Five is alot. A full car no boot room no pram room my kids already share rooms I'm so lost and way too fertile I feel so guilty feeling sad when it's the happiest thing to ever experience. I'm so lost