I only gained 1 in first 12 weeks ??
Im sure its just cause your clothes dont sit comfortable any more!
I'd not even say it was acctual weight gain probably from the bloating and water retention, couldn't be from baby at this stage seeing as it's smaller then a tadpole that's if it's even formed yet, but as the last poster said I'd watch your weight I actually lost around 17 pounds in the first 3 months and I'm 21 weeks now n has only gained bout 5 of those back, my midwife said loosing weight is not a problem but gaining weight (well lots) at the start is a cause for concern so I'd mention it to your doctor
in your first few weeks you will gain a few pounds, some people actually loose weight with being sick or feeling ill that they do not eat much. as your womb grows, at 6 weeks its larger in size also adding to your weight, but it pushes your intestines out making your clothes tight below the belly button. being pregnant you feel 'tight' in your normal clothes, even though you have not put on much weight. weight gain in pregnancy also is not rapid, but gradual. its normal to feel like this. monitor your weight, if you find you are gaining a lot in such a short period of time, speak to your doctor. also try light exercise like walking and try eat healthily. congrats on your BFP :)