Tummy time?

Hey guys my girl is 16 weeks and should be able to support herself on her tummy but she cant ive seem her try but she is just not interested she wont try to move just cried and hate being on her tummy. Ive tried toys and using a boppy to help her and its not as bad then but what can i do she can sit pretty well but slumps her head sometimes which im sure is bc she wont do tummy time but has good head control for the most part. She has her 4 month check up soon and i know dr will get mad if i say we dont do it much but its bc she wont try and just cries till i get her off her tummy.:(