PLEASE HELP THIS MOTHER........?

i have 2 & half yr old son,who always cries for silly reason and he wants the thing r anything if he asks,if not he start crying bcoz of this reason i'm very much irritated and started scolding him and hitted him some time whenever he does that. might b bcoz of this reason he started hating me he won't listen a singal word from me. now he is going to play school while coming back his grand pa(my father-in-law) will pick him up and he will b there in his house till his lunch. my co-sister also stays with them.she talks very nicly with my son as though she loves my son but truth is she and her husband really hates my son...i and my husband doesn;t have any bad felling about thier son who is 2 months younger than my son...co-sister and her husband never likes us till the day when i came to my in-laws house....now my son started liking them he listen each and every word of them without any cry and my son he thinks that i his own mother is bad and my co-sis is good...i don't know what to do... it really hurts me every much now i'm 4 month pregnant again every 1 say u should b happy but i can't every day i'm cring just bcoz my son is going far away from me...if they were good enough in there behaviour i would have no problem but i know they r not good......... pls help me and let me know what to do before it get late.....