Dear Ananda,
A lot of good advice about the posture, so I’ll skip the advice on the posture. I myself still struggle tremendously with the headstand and rarely attempt it and I use some props to assist me in getting there as well. We cannot always be good at every asana.
However, I want to focus my advice on the issue of a past life issue. This can indeed be a great obstacle in moving forward as we sometimes first have to acknowledge and work through our emotions connected to a karmic situation before a breaktrough can manifest. I say this because I have seen it so many times in my own life, it is only when the karma had been completed and that I have learned emotionally from that karmic situation that I will be able to move forward. Let me explain. I have been very apprehensive of doing the Chakrasana when I started yoga and something in me nearly always broke down when my own teacher would bring that asana into our set of asanas for the day. Anyway, I was fortunate enough to have a patient and very knowlegable teacher who one day invited me to her house and we started to work on this fear of mine, using guided meditations and some divination and direction from Spirirt Guides as well as some past life regression. It emerged that I was stretched over a huge wheel in a past incarnation for days until my back was broken eventually (middle ages as a witch) and the person who was the executioner was one of the other yogis in the class. Well, we came together and we had a interesting puja where I forgave and set this other lady free for her part she played in that past incarnation after she asked me for forgiveness. After that the asanas become very easy and I do it today with so much comfort that few people would belief me that I actually struggled with it at some point.
I think we are truely blessed when we as yogis have such opportunities to complete out karma with others under such amicable situations. I and this lady are today dear friends, she is much older than me and has really become like a mother to me as well. My advice, meditate on this, I feel you have all the necessary tools within available to discover something deeprer here and I am sure, from where you come, that there will be somebody who will be able to guide you through it.