A levels

...it would depend on your grades, PS, performance at interview, admissions test scores and any written work you submitted.

What course are you considering applying for and what are your other three ASs?

Medicine and 3 other subjects are biology chemistry and physics

Well, on the one hand I would say that Medicine is extremely competitive and you should avoid taking a 'softer' subject like sociology. But then actually sociology does involve some use of statistics and is easier to relate to Medicine than history.

Tbh, if you're planning on applying to Cambridge, I would strongly advise you to take Maths as your fourth subject and to take all four subjects to A2 if you can without dropping grades. For Oxford it's less vital to take four A2s, and they're less picky about the fourth subject. My friend is studying Medicine there now and she did Bio, Chem, Maths and English Lit. Other factors (mostly how well you perform at interview) will be far more important than whether you took sociology or history.

yeah I thought about taking maths and it would benefit me however I am too scared to risk a bad AS grade because everyone says maths is really hard

If you got an high A or A* for Maths GCSE, AS Maths (C1, C2, S1) will probably be fine. A2 Maths is where it gets hard.

If you're not planning on taking Maths and three sciences all to A2, focus on Oxford rather than Cambridge. Choose the fourth subject in which you will get the best grade, as they all have pros and cons:

Sociology: Use of statistics (relevant), some essays (so shows 'roundedness') easy to relate to degree in PS and interview but 'soft' subject
History: Essays (roundedness), 'traditional' subject but not obviously related to degree
Maths: Helps with other science subjects and in degree, relevant but doesn't show 'roundedness'