Hello there!
People (including in-laws and health visitors) do have a habit of telling what your baby should or shouldn't be doing at specific milestones - ignore them! Your LO is unique and will sit unaided when ready, and not when the books or other people say! Be patient, it will happen!
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I was told at 12 weeks that my LO was NOT teething.... I was then told at 4 months that he couldn't have a tooth cutting as it was too early - however, I assured the Health Visitor that she was wrong as he had cut 2 teeth!
Things will happen in good time! Enjoy your LO and all the milestones as they happen!
Tina