They're called vulval varicosities ie varicose veins in your ladybits and there's nothing you can do about them. They will disappear after you give birth. Warning: they leave your bits as baggy and wrinkly as an old man's scrotum, but this too shrinks away and you eventually return to normal.
If they're bothering you, try putting a maternity pad in your knickers, the counter-pressure seems to ease the discomfort.
I got them at 22wks when pg with DD, and just wore a sanitary towel in my pants for "support" (they disappeared within days of giving birth).
I noticed them at 14wks this time <sob> and posted on here for help & support - thankfully some wonderful ladies came back with some good ideas
I got some support tights from here which I found really good (make sure you check the sizing guides before you buy), I was getting really tired achy legs, but was fine after a day of wearing these.
But then I discovered I had thrush, so I thought that planning to wear tights for the rest of my pregnancy probably wasn't a good idea, and got the "V2 Supporter Maternity Belt" from here (it was the only place in the UK I found which stocked them). Attractive it is not (DH almost wet himself laughing when he saw it!) but it appears to work. As long as I wear it during the day, the "heaviness" has now gone (I tried not wearing it one day & it came back), and I'm not hiding myself from DH IYKWIM! Again, check the sizing & if in doubt it might be worth going up a size - I was a pre-preg size 12, so went for the small & it is very, very snug & I'm a bit worried it won't fit me when I get bigger!
oh, and putting your feet up will help too - they are varicose veins & caused by the blood not making it back up your body, so get gravity to help out by avoiding standing for long periods of time & putting your feet up whenever possible.