I guess I have been exercising regularly for over a year, now. I just don't feel right if I miss too many days in a row. I know for a fact that I would be one angry stressed-out person if I didn't exercise. I have a high stress job pleasing clients and face weekly publication/production deadlines... not to mention experiencing my fair share of office drama. I fear I would bite someone's head off if I couldn't relieve stress.
Before, I suffered with TMJ (subconsciously clenching my jaw and teeth) that caused serious pain and even dental problems. I anxiously overate sweets, etc. (alongside everyone else in the office) on particularly stressful days. In order to keep my job, I kept all my stress and frustration inside and took it out on myself in ways that were only harmful. I had heard that exercise relieves stress, but now I know it's true.
I'll not say I have had an exercise high, but I do feel accomplishment and pride when I'm finished working out. It's really become more than something I have to tell myself to do, but something I just need to do every day -- like brushing my teeth or bathing.
Keep it up. When I was more sporadic in exercising, I didn't really notice the good emotional effects. I think it's regular exercise that is the secret.
PS You said you're PMSing. Hormones bring on their own set of problems, and I think it would take a lot to overcome mother nature influenced mood swings. It can't hurt to exercise through it, but don't base your evaluation on what's happening at this time of the month. You're particularly vulnerable to bad moods right now. Girl power!