Toddler who dont speak in sentence neither calling papa mama

I m abit stressful and i need help and advise . I have a toddler who will be turning 3 year old soon but yet to call papa mama , used to call when is young but now no more and no proper sentence and i m so worried some say late bloomers as lo can say single word but not sentence neither answering questions , lo understand us and instruction but sometimes lo completely ignore us . I feel so depress why is my lo like this .. And i m so helpless , its just a matter of talking is there anyway to teach a kid to talk