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.