Thanks for replies about the phone. Sounds similar to my younger sis too, data only in sec 1 (last year). She spends her weekends on her phone though 
I'm currently in uni already. Hope this helps:
I took 3 sciences + geog + both A math and E math.
More science if: logic thinking
More humans (double humans) if: good grasp of writing. If dd or ds hates / dislikes writing essays of different lengths then this is not for them!
Both science and humans need memory work, so hope yall don't have misconception that humanities require more memorising than sciences.
Yeap physics O level is needed if you want to take physics in JC. In engineering courses (uni), physics > chemistry > biology meaning physics has been the most helpful to me, bio the least useful.
Phy - logic thinking, goes together with math
Bio - memory work + understanding
Chem - memory work + understanding
Geog - human geography I disliked, physical geography I liked!
Personally I disliked chem so much, that I almost took double science double humanities just to avoid chemistry.
But in sec 4 it got better because I began to understand it. Lab was also fun! There is much to memorise for chemistry, so I just learn to accept it and put in effort to remember all the reactions.
Eventually in JC i took physics + chemistry, rather than bio. I am stronger in math and sciences, writing essays I keep working on it.