The Game of Thrones timeline has always been quite confounding, but Cersei's pregnancy may be the worst instance yet that's thrown the whole series off track. Cersei's pregnancy was a major reveal at the end of season 7, and it spawn several fan theories online - from Tyrion betraying Daenerys to the idea that Cersei could die in childbirth (as her mother did before her). However, Game of Thrones only has two episodes left to go, and yet Cersei is still not visibly pregnant - which not only messes with many of these theories, but makes absolutely no sense when it comes to the passage of time in Westeros.
There have been inconsistencies with how much time it takes to travel in Westeros in the past, so messy timelines are nothing new to Game of Thrones. While it took multiple episodes for the Starks to travel from Winterfell to King's Landing in season 1, characters are now zipping down there in an episode or less. However, most of these instances can be fairly easily explained away as necessary for the narrative. There is simply too much going on to give characters the time they need to get from A to B, and in order to cut to the good stuff, the writers have had to make some sacrifices. Which is all well and good, but the decision to keep Cersei's pregnancy out of the timeline is far more egregious, because it's not just that we aren't seeing the time pass, it's that it's physically impossible and it messes with the greater story.
Cersei was far enough along to know that she was pregnant in season 7 - a minimum of a few weeks, but likely 4-6 weeks pregnant at that point. Since then, a vast amount of travel has taken place; during "Eastwatch", Jon Snow was about to set out on his wight-hunt beyond the Wall. Which means that they had the time to travel North, down to King's Landing (to show Cersei the wight), and back to Winterfell, then call their armies, fight the Battle of Winterfell, and travel all the way back to King's Landing to fight Cersei. Yet Cersei still isn't visibly pregnant. That's three trips from Winterfell to King's Landing and then some - trips that should be taking weeks, if not months. Cersei should be ready to pop, not barely showing.
The fact that Cersei's pregnancy seems to be a few months along, whereas the other events since the reveal should have taken almost a year, is deeply problematic. But there are possibilities for Game of Thrones' timeline issues other than bad writing. It's possible that Cersei has been lying from the start, using a false pregnancy to try and manipulate Jaime into staying with her when she realized that he was pulling away, and then to manipulate Tyrion into believing her lies. Now that she's with Euron, she could be using the same move to win his loyalty, convincing him a son of his would be king by lying about being pregnant. It's definitely not outside the realm of possibility for someone like Cersei, but having a woman as intelligent as her fall back on faking a pregnancy to get her lover to stay seems like it's just a different kind of lazy writing.
Another, sadder possibility is that she was pregnant, but lost Jaime's baby. This would fit with the valonqar prophecy and bring it back into play, and give her the idea of telling Euron that she is pregnant. Or she may be hiding it extremely well - long gowns, corsets, and cloaks could be keeping her secret, and it will be revealed in a dramatic moment in the next episode. Finally, she could have lost one baby and become pregnant again, thanks to Euron, but that seems unnecessarily confusing, especially without any scenes of grief over the loss of her child with Jaime. This also doesn't fit with her previous reactions to becoming pregnant by someone else - she "rid herself" of Robert Baratheon's children in the past. Whatever is going on with Cersei's (potential) pregnancy, only time (messy, unrealistic Westeros time) will tell.
Game of Thrones season 8 continues on Sunday, May 12 on HBO.