Oh mama, I really feel you, my second one had very similar signs at around that age, the mouth breathing and snoring, and I was so worried too! We ended up seeing a paediatric ENT who checked for enlarged adenoids and tonsils, which are actually a very common cause of sleep apnea in toddlers, so that might be a good first step for you. My friend brought her son to Khoo Teck Puat Hospital and said they have sleep apnea screening there, and she found the consultation quite thorough and helpful. I also heard there are home sleep testing options available now, which is more convenient than an overnight hospital stay, and some are quite affordable. Do also check with your PD first though, as they can give a proper referral to the right specialist for a child your LO's age, hope you both get some rest soon, hang in there!