When you are depressed it is really easy to blame the depression on things in your life... that just means that even if you can find reasons for the depression there could still be some underlying cause... or not...
Pregnancy is often a time of diagnosis for BP, and hormonal mood swings have been linked with BP but the link is controversial - the whole bipolar spectrum/ soft bipolar thing is just one theory to try and describe what appears to occur - they may find it is right or it may be a load of crap - time will tell.
Regardless of bipolar, bipolar spectrum, unipolar whatever... if the depression is causing significant problems in your life you need someone to manage the treatment, they will need to assess you to decide what is the best treatment to try, but these things are often trial and error... be patient.