Pregnancy is a really weird thing. I think I know the pains that you are talking about because I remember having pains there too and there was really no cause for it except for "random pregnancy pains", and I think it's normal, but you should call your doctor just to make sure that everything is ok. If you don't feel right about calling him, you can just speak to a nurse about it and I'm sure they could advise on whether or not it was serious enough to have your doctor check you out. At 25 weeks, you may not feel so big, but there is a lot going on in there that can pressurize whatever is underneath the baby.
I have sciatica both when pregnant and non-pregnant. I don't think can effect just your vagina....it might, but you would feel pain elsewhere too. Right now I'm 9 months pregnant and my back condition is effecting my entire lower abs and killing my pelvis. If you start to have sciatica pains, it will be painful sensation that runs down usually just one of your legs to your knee and you will feel something like a needle sticking into your lower back. This is because your sciatic nerve runs from there through your hip down your leg. Most of the time it's not going to effect both legs or go past your knee, but if it does, it's usually when you are farther along in the pregnancy and a chiropractor usually can give you some relief or suggest that you wear a support belt.
I found that getting one of those long body pillows for rest and night time really helps will all of the pain, including vaginal aches. It helps relax all the muscles around your back and your pelvis and supports your growing belly.
I hope everything is ok.
