Lizzy was right. The shower just is not big enough for 3. You find some positions that are doable, but not that are fun. You just are better off waiting until Lillian is fully digested.

Besides, you can still do it perfectly well in bed. Maybe some positions are still too much trouble, but doggie works fine. With Lillian below her like an oversized pillow, she presents to you in a most exciting manner. In fact you get off right away. It is not wise to leave her unfulfilled, so you keep plunging, a decision with its own costs. You are more exhausted than you thought, and have not come close to coming even after Lizzy has come twice. You are just excited enough to be determined to get off and so keep working, to Lizzy's pleasure. You are not sure if she has come 6 or 7 times by the time you finally succeed. It is long enough that you are thinking that no good deed goes unpunished.
But as the two of you cuddle and fall asleep, you have to admit it has been a most satisfactory day.

But the next day starts out badly. When you wake, you realize that there is still a large amount of Lillian in Lizzy. The bulge has gone down a lot, 3/4 easy. But her belly ought to be flat as a pancake. You touch it and it feels wrong too. Something weird has happened here.
You had best see somebody about this