Fantastic you have already spent time considering the options and identifying a new career. This is often the most difficult stage for people and this will give you the source of your momentum.
But first let's consider what's holding you back.
I'm not sure that you have really bottomed-out just what is causing you to feel that you want to change careers. You appear to like the role as a Research Associate so why change? You must be feeling that there is something missing at the moment - is this permanent? Even though you are getting plenty of satisfaction from what you do now, your feelings seem to be telling you that a more satisfying career is possible.
Start to consider what it is that is missing from your current job and list out all the things you don't like - so far you've mentioned only the ones you do. Does your idea for a future career give you pointers towards what is missing? Work out why a very different career in mental health appeals - what does it offer to you? Thoroughly explore the output from this analysis with a person who knows you well and establish what needs to change. You can use these things as motivators to move forward.
Explore all the things about your new career that will satisfy you and use these as reference points to encourage you in your journey. List out those things you will achieve and visualise what the new career offers. Place yourself in the new role, feel the difference and remember how this feels if you start to have doubts or need motivation.
This week set up to meet a close friend to discuss what you enjoy and don't enjoy about your current job and use the time between now and then to start listing the things to discuss. As you move forward use this person to encourage you to keep on track, set a timeline for changing your career and establish what you need to do to become an Assistant Psychologist. Meet people who are doing the job now, get a feel for how well the job fits and keep referencing that timeline - if you don't want to, ask yourself why or better still get your friend to ask you why things aren't progressing.

Follow us on