I know I should be used to it by now, but it never ceases to amaze me how horrible women can be to each other!! What has the OP actually done to warrant all these nasty comments?
OP, I actually quite enjoy a wedding from time to time, but in your circumstances rather than making excuses, I would simply put out a message to the whole family, and all your friends, saying something along the lines of:
For all of you who are getting married in the near future, or make plans to do so in years to come, I really hope you won't take offence, but I've decided to be upfront, and ask you to please save yourselves an invitation, by not sending one to me and my family.
No! I've not lost the plot, but I really don't enjoy anything about weddings, and find the whole thing really stressful, from the dressing up, to eating fancy food, (which all too often costs you a bomb, and ends up getting wasted), having to shop for gifts, arranging transport, find suitable outfits for the kids, and then keeping an eye on them the whole time, so that they don't spoil their clothes, or annoy people. So I figured that if I let everyone know upfront, it will save time and hassle for all of us.
Oh, and just to be clear, I have absolutely nothing against marriage, and wish all of you that decide to go for it, every happiness.
Hopefully by doing this, you might have to answer a few questions initially, but once the word's out there, you shouldn't have to deal with it anymore.