Hi Creative,
What you are experiencing is one of the negative outcomes of our brains being simple processors.
Our brains are hardwired to fixate on traumas, pains, stress, etc. and to filter out the "irrelevant" aka times we were safe or things that make us feel safe. That is because our brain's priority is far different than our emotional priority. Our brain's priority is your survival, it does this by remembering unsafe situations in order to process them faster and get us out of the situation sooner by reflecting on how this was achieved in similar situations in the past. Our brain takes a lot of energy to run, so it is constantly looking for ways to make shortcuts. This is why traumas are more often repeated in our minds versus the good times. Good times don't threaten our survival and are, thus, deemed less important for the brain to remember.
There are ways to harness this innate focus of our brains, though. I highly suggest looking up the Pocket Psychologist on Facebook. She is so wonderful at breaking down how the brain works and then providing you with strategies to reign the brain back in. It does take practice to engage the prefrontal cortex, our thinking brain, over the basic brain (which is simple and looking for shortcuts), so if you feel you are struggling and your brain hurts at first that is totally normal - that is the feeling of growing new neural pathways, and it gets easier as you continue to reach for those new neurons and build strong connections to them for easier and quicker retrieval later.