window.history.pushState removing my part of URL

I currently have below link
http://localhost:3000/A/B

When i use window.history.pushState(null, null , './pg-<%=params[:page]%>?pgsz=<%=params[:pgsz]%>') it removes B part of my URL and then append the params to it.

And if i use / instead of ./ then it completely removes /A/B

How to just append my params to the end of my URL and keep changing only the end part.