Yes a lot of what you are experiencing could potential be from bipolar, such as rapid cycling (which I experience) where mood swings can change at an extremely short rate of time as you described. There are several types of bipolar and each person's experience varies regardless. However only a psychiatrist could provide a specific diagnosis but it would be worth seeing one.
Yes I agree with iladvocate... I would see a psychiatrist and talk to them about it...
It sounds like your moods are going from depressed to normal but quite rapidly..we do have ups and downs during the day where we feel depressed then back to baseline then to a better mood, then back to baseline.
It sounds like depression, but with the rapid switch it could be cyclomythia. It's impossible to say. It could be that you have depression and a way of coping that you are using i.e distraction could be what is cheering you up! A lot of people feel depression is at its worse in the morning and gets better slightly through the day.
I think you should seek treatment, whether that be, medication, therapy, natural remedies etc.
I hope you feel better soon!