My husband has cyclothymia, which is a mild form of bi-polar. It is characterized by short periods of "up" mood (for a few days or maybe a week or two) followed by several weeks of even a couple of months of depression, followed by "normal" for a while, then the cycle repeats.
His depression was diagnosed many, many years ago and while not crippling, it's pretty obvious - crabby, anti-social, sleeps a lot, can be hungry but doesn't enjoy what he eats or has no appetite, no sex drive, withdraws from relationships, hates his job, the whole world sucks, complains that he's fat and tired and worthless and stupid and lazy and bored, etc. Sometimes it hits like a freight train and I know the The Depression Monster has arrived and taken over. One day I talked to him in the car as he was on his way home and he was fine, making plans for dinner etc. Not 30 minutes later he was home and in bed, and that down period lasted almost 10 weeks. Other times it takes me a few days of crabbiness to realize that it's not me, it's not even him, it's the illness.
The hypomanic side was harder to see - sometimes it looks like ADHD (which he also has) and other times, he just seemed to be a much more energetic version of himself. During these periods he's very happy, productive, energetic, social, starts lots of projects, and seems to be firing on all cylinders. The balanced side of this cycle is how I am all the time and what I fell in love with. But the dark side of the hypomania is there too - these are the times that he makes major impulse purchases (cars, motorcycles, boats), quits his job to pursue something commission only (which never works out), or, earlier in our marriage, slept with other people.
He is now and will forever be off of anti-depressants in the SSRI class, which used to make things worse. He has also had bad luck with ADHD meds so he doesn't treat that with medication anymore. He was on lithium for several months last year but then had a reaction to that and has been on Depakote ever since (both are old-school medications that are fairly easy to manage vs. some of the newer ones).
When bipolar is crippling it's pretty easy to see and diagnose - but when it's mild it can be very hard to get an accurate diagnosis. Lifestyle changes certainly help but just about every study I've ever seen says that with a cyclical mood disorder, medication it almost always a part of regaining control of the patient's life.
The complicating factor for diagnosing anything cyclical for women is that we have our hormone cycles to deal with, so do be careful that whoever you see for a further diagnosis has a lot of experience in figuring out the difference between mood swings caused by a mood disorder vs. hormonal changes. If you've been keeping a log then hopefully any relationships between your mood and your cycle will be pretty obvious.
Best of luck to you - I have to say that having my husband's illness correctly diagnosed took him 25 years (he saw his first psychologist at 15, was diagnosed with depression in his 20s, ADHD in his 30s and with cyclythemia at 40) but he finally feels "normal" and it's been a huge help to me to know that we're dealing with an illness and not personality traits.