It is not uncommon to get depression during pregnancy so you're not alone. There is always help at hand and I'm glad to hear that you are keen to seek treatment. There are a few ways you can go about this. You can see a GP or a Polyclinic doctor to get a referral to see a Psychiatrist who can then assess your condition and tailor the necessary treatment for you, especially now that you're pregnant (a lot of medications, both psychiatric and non-psychiatric, are contraindicated in pregnancy). If you prefer a more direct access, you can always seek help at the 24-hour Emergency Service in Institute of Mental Health (IMH) which is located at Buangkok Green, in between Hougang MRT and Buangkok MRT.
IMH's address is:
Buangkok Green Medical Park
10 Buangkok View
Singapore 539747
The IMH main enquiries / general line phone number is: 6389 2000 (24-hour)
If in crisis, there is also another 24-hour hotline you can call, known as the Mental Health Helpline: 6389 2222
I sincerely hope you get the care and treatment you need to get better soon. Hopefully others in similar situation or others who know someone who require mental health help will also find the above information useful.