Help please! Bride asked for my address to send invitation but i haven’t received anything?

Why don't you call to catch up? Ask her how wedding planning is going. If you're off the list, she never sent STDs or anything major has changed I would think she'd get the hint and let you know. But being that she asked for your address and told you to expect a save the date, I don't think there's anything wrong with asking more directly, especially if it's important to book accommodations early etc. It could easily be that the STD was lost in the mail.

We sent our invitations 3 months ahead of time (December for a March wedding), to give people enough time to plan for travel, but I've also received invitations for weddings within a month of the wedding (even after having got a save the date far in advance).

I would wait at least 2 months before the expected wedding month before freaking out over it, as I assume some people don't want to send them out too early in case anything happens (people forget, they can't RSVP until closer to the date because they have to figure out scheduling and travel plan possibilities).

We had a couple invitations returned but also we started reaching out to people about RSVPs about 1.5 months after we sent out the invitations, then we found out some people never received an invitation (wrong address or other), but they never asked us about it until we were hunting down RSVPs. So hopefully the couple tries to hunt down pending RSVPs!

I think things happen and it's easy to get caught up in the rush of things. If she said you would be getting a save the date and invitation, I don't think it would be rude to ask about saving the date; you could frame it in a way like "Some things might be coming up in the next few months and we want to be able to celebrate your wedding with you. Will you be sending out save the dates so we can block your wedding weekend out on our calendar?" or something like that so you can get the date in case they haven't sent anything out yet.