7 year old soiling problem

Hi

My 7 year old up until about 4 days ago would go to the toilet fine. Now for some unknown reason he's been soiling his underwear 3-4 times a,day. I thought constipation but he had a normal poo this morning but has just had another accident. Its not a full poo but a thick smearing (sorry if tmi). Really don't know what to do. Really upsetting me ad at my wits and