For a 3-month-old baby who is congested and seems more tired than usual but does not have a fever, the best way to reduce nasal congestion is to use a saline solution like SALINEX, HYDRASENSE, or SINUS RINSE PEDIATRIQUE. It's generally a good sign that there is no fever, which means a medical consultation may not be immediately necessary. Make sure to keep the baby hydrated and allow them to rest, as their body is likely working hard to fight off the infection. If symptoms worsen or last longer than 7-10 days, it may be a good idea to seek medical advice.