You said he can speak and play alongside others which to me suggests he doesn't have autism or aspergers.
Sorry, vickylu, but you have been badly informed here. The fact that a child only engages in parallel play at this age and is not beginning to play cooperatively is a cause for concern and it is very common in children with ASDs. Other qualities of play to look for at this age include lack of imaginative play, insisting that toys cannot be used except for their expressed purposed, e.g. you can only use a toy phone as a phone, never a toy banana, and becoming angry or anxious when others, including adults, try to direct the play.
My DD1 was able to speak in sentences before her first birthday and this is more common in children with ASDs. Asperger's Syndrome is defined by many as Autism without speech delay. Very early reading is also a sign. My DD1 taught herself to read just after her second birthday.
Preschool SENCos should be able to inform you of anything unusual they have observed but they are rarely qualified to do more than that. I'm not aware that practitioners can refer to paediatricians for assessment but I am happy to be corrected if that happens in other areas than my own.
Food issues are also more common in children with ASDs, including eating around others, problems with textures and food being mixed together. This needs more careful handling than with NT children as the rule that a fussy eater won't starve themselves doesn't necessarily apply when a neurodevelopmental disorder is present.
The key to supporting children who have or may have an ASD is usually managing their anxiety. Lots of children seek to gain control wherever possible as a way to manage an unpredictable and overwhelming world. Stable routines, clear and calm behaviour management based on rewards rather than sanctions can help a great deal, as can ensuring that daily plans are explained clearly with regular reminders and kept to wherever possible.