Struggling to fall pregnant

Hi guys iv been trying to conceive for about 1 year now I’m already a mum of a 4 year old and iv just put him into preschool and got clucky but have had no luck at all have been to the doctors and was told nothings wrong just to start taking iron tablets as my iron levels are never the best and to keep doing what Im doing it’s been about six month since going to the doctors. When/ should I go back to the doctors and tell them it’s just not happening any help or suggestions please would be much appreciated? :) xx