Please don't mistake me, everyone has downtime. Monday blues happens to me as well.
I would like to question whether your Monday is a "Monday blue" or it is a "Blue Monday"?
Do you like your job and foresee doing it for 10 more years?
Does it still align with what you were thinking?
I am an Electronic Engineering Graduate from World Class University, having scholarships and awards. But it does not mean that I love Engineering till now. Our trajectory can change according to our life experiences, friendship and social activities.
Our job is like our cloth, it needs to be fitted in the correct sizes, designs, cutting and personalities. Is your current job reflect who you are? It is just a life parachute that you secure your daily expenses? There is nothing wrong to stick to a job you don't fully love, but you need to acknowledge it and if possible, try to find a job you love slowly.