Ok that definitely sounds like an energy deficiency in that case. I suppose you ate some pork before as well where fat might be more plentiful. If you want to stick with pure beef (as in meat) there's still tri-tip that is very fatty and if you have a slow cooker you could go for some slow cooked brisket in beef stock.

Other things to consider is trying to see if you can get fatter beef like black angus or wagyu, though these might be a bit more expensive as well.

If you really need the fat consider clarified butter (ghee) like others already suggested. Most people with allergies (especially lactose) have no issue with ghee as it is 99.9% pure fat.

Then there's still raw milk which might suite you better than pasteurized as these still contain many of the micro organisms that will help break down things like lactose, but i would start really small.

In the end you should feel good and you should not force yourself into anything if it doesn't sit well with you. If that means adding back in things of what you ate before than that is ok.