I don't want to go

I don't know what to do....
I have a friends wedding at the end of April it's going to cost my SO and I over $800 to get there and to pay for accommodation. 
But Iv found out that the bride has invited my sister to her hens night and not me, yes I'm almost 6months pregnant but that's beside the point.
what's the point inviting someone to a hens night if they aren't invited to your wedding but not inviting a person who is going to your wedding? 
I don't want to go anymore and would rather save my money and spend it on out of town doctor appointments and my house hold bills.
UPDATE 
So I over reacted turns out I was invited to the hens night my sister 
just hadn't given me my invitation. 
This all happened on the 19th-20th April 
But I didn't go not because I didn't want to but because I was rushed to hospital the Wednesday before the hens night. I started cramping at work and my cirvix was opening when I got to my hospital. I was airlifted to a big city hospital that night while in flight my waters broke. 
The nurses managed to stop my laybour but we still lost our son Thursday afternoon. I had him naturally like his sister back in 2015 who was also still born. 
I was in hospital till that Sunday so missed the hens night and my SO and I didn't go to the wedding the next weekend because we couldn't make ourselves go and to go back to the big city so soon we wouldn't have enjoyed ourselves. So we stayed home and organised our sons funeral for the 1st of May.