What are the best A-levels to choose.

STUDENTGCSE2017

I'm picking physics and maths - definitely. I want to head down that route and possible look into astronomy, or even architecture as I love art.
However I need a 3rd a level. I'm in this dilemma because:
-I am awful at chemistry and biology
-I work at a 6 in maths so I would struggle at further maths
-subjects I do enjoy such as art/IT, in my opinion wouldn't be enjoyable for 2 years
-I am also very shy so I wouldn't fit in with politics or the English side to things

So yeah... I'm completely confused. To be honest, geology doesn't seem bad. I think it looks like at interesting subject, however I didn't take geography at GCSE and my school didn't do geology so I could completely fail the course.