When to seek professional help?

My fiancé and I have been trying for 18 months, he works a lot and is a chef (I've heard the heat does not help with his little guys!) so I'm not overly worried as we do not have sex a lot because of his hours but I always make sure we do around my ovulation dates. I was on contraception (pill, patch and then injection) for 10 years before coming off of it. 
Does anyone recommend when we should go doctors to see if there is anything wrong with us? Is anyone else having the same issue as us??