Recurrent Mouth ulcers in the past

Hi, 2 months ago I started having recurrent ulcers in my mouth and tongue (1-2 at the same time-normal size-after 4,5 days were disappearing). I had full blood count and everything was fine – for 10 days no ulcers again. After my holidays then I started having again ulcers in my mouth and tongue and my GP gave me Corsodyl mouthwash which was perfect – the 2 ulcers I had disappeared and never again appeared. I have no ulcers at all for 3-4 weeks now but I’m just very anxious cause in internet it says a lot of serious illnesses are causing ulcers and that is why I’m a bit concerned. I have also quit smoking on January (that might be a reason why?) and I was having exams as well which means I was stressed. One GP told me if I’d like to have more blood tests (std related test) but I haven’t. What do you think?