I have failed Continuously in 4 Prelims. I have fundamental loopholes in my preparation and my studies. I haven't taken any Foundational Coaching and rely on Test Series. How should i improve upon my Mistakes ?

Clear your concepts first. For that, go through standard books. Don't jump in test series first hand. Over reliance on test series will only harm you. Test series should only be attempted after you have covered your syllabus comprehensively and understood it properly. And when I say cover your syllabus comprehensively and properly, I mean each and every corner of your notes should be known and understood. Each and every corner. For this, you need to revise the same notes over and over again. You can use topper's notes for that. I have been using Mandar Patki's notes since 2020 and cleared prelims every time since. Was getting 119+ this time and cleared IFoS too.

Use the same strategy for Current affairs. PT365 is the most reliable of the lot. Take it and cover each and every corner of that pdf for major subjects - Economy, Science, Environment, IR atleast. Go through the same thing 7 times, 8, 9, 10 times over and over again till you don't want to do it anymore and then do it once more. This is the formula of clearing prelims.