Tummy Time, Sitting up, and Crawling advice please?

Madisyn is 6 months old. She loves to roll over and over. But when it comes to just tummy time she screams her head off until i pick her up. Any ideas on how to make it more fun?? Also, She will sit on her own, if i put her in position...If she falls or wants to sit up i have to pick her back up, she can not figure out how to do it on her own. All she does is lift her legs in the air and bring her chin in and grunt as if she is doing stomach crunches... When did your child learn to do it on their own or how did you show them/ teach them.. Any advice?? Finally... Because she does not like tummy time, she is not very close to crawling. Now i understand that 6 months is a bit early for a crawler, but she wants to move, she just wont take the time to learn. She does nto get into positon. she is either on her hands, or her toes, neither at the same time. How do i help this along too?? I am a new mommy and need help!!! thanks...