1. PS+DS= above 35, less than 40
Check the answers to see if you make silly mistakes like forgetting using negatives, fractions etc. when plugging in. Backsolving helps too and becareful of obvious "A+B" answers for DS. I think you encounter "algebra intensive" problems when you get to harder problems so if you do plugin you should be OK for the most part. But if you want to get a good quant score you gonna need to do them sooner or later. Surprisingly combinations/probabilities were never that big of a deal when i took the exams - i saw maybe 3 total from 2 tests.
2. SC= It just depends on my mood, sometimes I get 70% right, but most of the the times 30% why??
I hate to guess but i think you are not getting the core grammar right so sometimes you might get some "lucky" corrects by "sound" - it is like what happened to me when i kept scoring 28s. know your idioms,tenses,FANBOYS,subject verb agreement.
3. CR= Though frequency of getting these questions wrong is high, I like this topic
You have to read paragraph carefully. DO NOT fall into traps that uses outside info unless it is a hypothetical question. The books help a bit in planning the attack but unlike SC there's no "blueprint" to follow besides the number of types of questions are asked and it is mostly up to you to understand the passage...
4. RC = makes me sleepy, cant focus for long. usually get only 50% of the questions right
RC is tough too - you get the tactics from the books BUT since passages differ you have to analyze the most of it. There are basically 2 ways to do this - read the passage then answer question OR skim it and write down important facts - usually read couple of sentences per paragraph. I hate 2nd option because i find myself reading the parts i missed to double check my answer anyway - it is up to you though. Again there are only a set number of questions asked and it is up to you to understand the passage.
If you are applying for next year i think you can delay the exam till june and still be OK. You could still do may then do june but if you want 700 i think you got a lot more work to do.