How far along am I and am I having a miscarriage?

This isn't my first pregnancy, I have two children. My cycle has always been very regular and my pregnancies have been very straightforward. I knew I was pregnant before my missed periods. However this time I'm at a loss. Firstly, I have only had maybe 4 periods since my son was born since I'm still bf. So I had my first one about a year pp. My last period was September 30th but it was a few days late and just seemed different which isn't normal. Then around October 17th I thought my period started again. I would have light to moderate bleeding for a day then nothing for a day then bleeding for a day. This continued for a little over a week. I had spotting last night. And I took a test today for the first time not thinking I was pregnant but its positive. How far along do you think I am and am I having a miscarriage?