Before I go into this post, I want to be clear that there is nothing actually "wrong" or "incorrect" about thinking positive. In fact, honestly think telling yourself positive things can help you turn around your mood, if said repeatedly and mindfully.
However "should-ing" yourself is the first red-flag that its not going to be very a very effective practice, second of all thinking positively isn't the only way to feel positive. In fact, removing judgment from our thoughts and our language can be even more beneficial in many way. The labeling of positive and negative, can get anyone into a trouble/moral dilemma and stuck in "black and white thinking.
By having attachments to the outcomes of events and situations we are in, it can take us away from the purpose of the lesson from the event and the event in it self. Blocking us from feeling our feelings, since we may try to demand ourselves to see it "up-side". So take a deep breath and feel your feelings.
I do believe that speaking to yourself with affirmations, that speak abundance and health into our life is one of the best "positive thinking" that can be done by any individual daily. In other words, there is no way to "make it all better with a positive thought", its more about creating a mindset of abundance and to move cultivating a midset that is moving you closer to the things you want in your life.