Realm wide lag

My friends and I have been playing on this realm for the past two months with no lag or bugs, but sometime recently we’ve all been experiencing serious lag, up to the point where no one really wants to play anymore because of it. We have a backpack mod and a furniture mod installed, but that’s it. We haven’t had a problem with those since I installed them. I’m at a loss at what it might be and I just need some answers.