2 yr old ...CONSTIPATION!! HELP?

my little girl hasnt had a bm in 3 days , she's crying on the toilet seat 'mommy help it out' she's in so much pain. i have tried EVERYTHING and i HATE suppositories from bad experience so i have not tried them. i brought her to the doctor today as she was up all night last night crying. he said suppositories is the only thing left to try and they usually dont dissapoint. could you comment with experience or how i should approach doing this? how i put it up? need help ASAP! thanks x