If your forget-me-nots are not blooming, then there are three primary reasons contributing to the cause,
i). too much sunlight – as mentioned earlier, forget-me-nots grow in partially shaded areas, exposure to excessive sunlight translates directly into limited success with flowers. Instead of producing flowers, the plants will end up burning or wilting under the hot sun.
ii). improper fertilization – the soil needs to be fertilized to work in the essential nutrients. But too much of something can make things worse. Similarly, if you overwork fertilizers in the soil then forget-me-nots won't bloom.  So carefully schedule your fertilization routine to twice a year.
iii). dry soil – forget-me-not loves bog; thus, super moist soil is what we are looking for. Make sure to keep the moisture levels up by watering during hot, humid conditions when there is not enough rain. Dry soil will majorly contribute to a plan that does not five flowers.