3-month-old Behind On Milestones

Hi all, my baby is 3 months old (2 months old corrected since she was 4 weeks premature). Right now I feel like she's behind on many milestones even for a 2 month old. She can hardly lift her head at all during tummy time, doesn't notice her hands or do anything with her hands, doesn't really focus on me when I'm talking to her (sometimes she does but usually doesn't) and very rarely smiles. Is that a problem? What can I do to help her catch up? Should she see a doctor?