Happiness is born in the moment. You only ever find it in the now. Which does not mean that you cannot enjoy memories and anticipations, but find those too in this present moment, for that is where they can nurture you.
When you are happy you are in the flow. Not happy? Something is not flowing. Don't compound the problem with worry and judgement, but admire your ability to notice. Admire what you notice, that stuckness, even if you have no idea right now what is stuck. Your admiration can easily transmute into love, and love frees all.
Each moment passes and with it the happiness of each moment. Let it go with the moment and, in your awareness of having moved to a new moment, let the happiness this moment offers reveal itself to you.
Don't judge yourself - ever. Forgive yourself and all others just as soon as you can. But recognise the flow of life; sometimes you have to let that flow bring you to forgiveness in its own time.