Question: I am not a happy person, is there a way to change that? That is honestly my whole question. I am pretty much fine in every way, I have a good husband, healthy frum kids, a decent job, we have decent parnassah, are part of a nice kehilla etc.. Yes, I have the stresses of every frum family but nothing major. With all that said I am a pretty moody and cynical person. If I am being fully honest, I always have been. I sometimes get jealous of others and imagine they must be so much happier. It's been bothering me that I can't just be happy and it's something I have been struggling with a lot recently. I had an epiphany that maybe it doesn't have much to do with anything in my life and more to do with my personality. Are some people just naturally happier than others? If yes, is there anything I could do to change my personality? If this isn't true, what is it really that just won't allow me to be happy?
Yes, it is quite possible that just as there are differences among people in variables like height and eye color, there are also variations in temperament. Temperament refers to innate traits that we are born with and one of these traits is mood. Some have a disposition to have a happier chirpy mood while others are naturally more dour and pessimistic. Rav Chaim Vital as well as others discuss the four types of personalities and struggles that emanate from them: aish (fire), mayim (water), ruach (wind), and afar (earth). Those who tend towards the "afar" (earth) side of things will struggle with moods. 
As such, the first thing to keep in mind is not to blame yourself for feeling unhappy. This is a natural nisayon that came to you through no fault of your own. That being said, there are several things that one can do to improve mood including the following:   
Fulfillment and accomplishment. Happiness comes from experiencing your own growth. When one can reflect on what he or she has accomplished over time whether in things like  raising children, finishing a mesechta, or completing a project, one feels a sense of meaning and purpose. This is authentic happiness, which makes all the sacrifices experienced along the way to be worthwhile. 
Giving. Happiness comes from giving to others. People enjoy contributing because it both helps others and it feels good. When one is able to put a smile on someone else, this somehow gives us real meaning. The Rambam (Hilchos Yomtov 6:18) writes of the importance of experiencing simchas yomtov by providing to those less fortunate. He says that those who celebrate yomtov with their family and do not include the poor and depressed are not experiencing true simchas yomtov. 
Connection. Happiness is about spending time with friends and family and feeling connected. Research consistently shows that we are social creatures who need connection with others to thrive: in fact, loneliness is a tremendous risk factor for many negative outcomes. Rav Wolbe (Alei Shur end of 2nd chelek) discusses simcha as emanating from connectedness to both others and to Hashem. 
Perspective. Lastly, happiness is about cultivating and developing the proper perspective. We may not be able to control our daily mood, but we can train ourselves to develop an overall positive perspective. For example, if a person has a stressful day, they can reflect a bit on the positive and focus on the macro picture and the gifts that they do have such as wonderful family, caring spouse, or whatever else he has to be grateful for. Practicing this on a consistent basis can help shift overall mood to feeling more content, grateful, and accomplished. 
May you merit a true Simchas Yomtov!