Pop and see a local osteopath and get it checked out (GP's may be able to help but will more likely refer you to a physio (on a waiting list) for assessment in case it could be something like RSI, tendonitis or carpal tunnel syndrome.
If the sewing is irritating it then rest is the best option, at least taking regular breaks.
Ice packs can help with the pain, Biofreeze is good too, comes in a roll on.
Voltarol gel is pretty good too at reducing pain and swelling and you could try an anti-inflammatory.
Splints are pretty good, Boots do a good one, it's black and doesn't restrict your hands so much.
Seriously though, if the sewing is causing a problem you need to address that and get yourself better rather than just treating the symptoms and carrying on. If left to get worse it could become a serious problem.
Many places have support groups where people may be able to give you more tips and advice.
There's some more info here...
http://www.nhsdirect.nhs.uk/articles/article.a spx?articleid=314#