How to afford all of these wedding showers, wedding gifts, baby showers, graduations?

When I was in your situation, I just sent cards. I looked up quotations to handwrite onto the cards, and I added personal thoughts or other things to make them nicer. Walgreen’s has nice-looking blank cards at about $1.50/box of twelve, and dollar store sell specific-occasion cards at 2/$1.
Send regrets (phone or write to say you’re sorry but you can’t be there) for the showers and for any other parties you can’t afford to attend. Remind yourself (and others if necessary) that gifts are never required or owed. It feels strange to send no gifts, but sometimes personal circumstances make it necessary. Depending whose party it is, explain that your finances are too tight to allow you to attend. Most people understand that situation nowadays.
If possible, make offers to help such as doing behind-the-scenes work for some of those parties (you could help serve food or you could look after children during a wedding or shower, for example). That way, you’ll be with your family even though you can’t attend as guest.
Try to keep cheerful about this. This stage will pass and one day you’ll be in better shape to afford to do more.