my personal take on this would be relax and accept things as they are. you dont have to feel always sexy, there can and should be times when you feel sad, angry, happy, tired, funny etc. if you fight your natural state of mind or emotions resp. this can easily backfire, it is like pouring oil into fire. What oyu can do to change your mood is finding specific things which trigger that feeling you want, e.g if i feel tired i do some work out and for me it is an energy boost, or if you feel too much tension then find something to release (ok even THAT might work), breathing exercises could be a good idea, and so on. generally try to look were you are with your emotions, accept them and look for what you need to change them to the desired state.
for your mental work you might want to try this, it is called tapping and a combination of autosuggestion and acupressure:
http://de.youtube.com/watch?v=6i33V2EcVlY
and/or this, the Circle of Excellence, a NLP technique:
http://de.youtube.com/watch?v=QJgxm9Bo8IQ
and/or this:
Richard Bandler uses this technique for getting rid of any phobia. It starts with you putting yourself (mentally) in the situation that causes the bad feeling. You look inside where it starts from in your body, can be your stomach, your throat, where ever. the feeling might start at one point and then expand to other places of your body, realize where it goes and look at it as a circle of energy that is either going in or going out. give it a colour. take your time to visualize it. now that you have a spinning flow of energy that causes you a bad feeling, simply turn it the other way round and change the colour to one you like. visualize the energy circle getting brighter and more intense and moving faster and faster and while realizing this you immediately start to feel better. when you are near the peak of feeling good you anchor it with a gesture like clapping your hands or snap your fingers or say a word like "go!". step out of the situation, think of something else for some time and then step in again and repeat. do it several times until you get the wanted success.
hth.