Try to do more tummy time everyday. If baby gets tired, let him rest then try again. I try to accumulate total 0.5h tummy time each day at least. When doing it without pillow initially try putting baby's hand together below his chest for extra support, it'll be easier for him than the push up position.
its normal, my baby 5.5mths and cant turn yet. but she can sit unassisted for a short period. some baby skip turn, some skip crawl. each baby is unique! dont worry mom, let them grow as their own pace.
my daughter also never do tummy time, she hated it. Nothing to worry. Every child is different.