Hello,my Baby Is 6 Months 2 Weeks And Her Neck

Hello,my baby is 6 months 2 weeks and her neck is still not strong enough,I still support a little,and her bones are making a crack noice,even when she stands her feets tremble,can it be that she need calcium,or whats the problem.and again since I'm so worried,I went to the pharmacist and was given calcimax syrop to be given 2.5ml (150ml) three times a day ,is it ok to do that?