I've watched people deal with this and it's genuinely rough - that first trimester nausea can be relentless, especially when you're trying to hide it. The bathroom runs are tough to explain away, so a few things that seem to help: eating something small every couple hours (crackers, ginger biscuits, whatever you can stomach) keeps your blood sugar steady and often reduces nausea spikes. Keep snacks at your desk so you're not scrambling. Ginger tea or candies actually work for a lot of people - not a cure, but takes the edge off. Peppermint can help too. Fresh air and staying hydrated matter more than you'd think, so if you can step outside for five minutes between meetings, do it.
For the bathroom situation, you might frame frequent trips as needing water breaks or dealing with something generic like stomach sensitivity - people are usually too wrapped up in their own stuff to connect the dots. If you're feeling really desperate, some folks find that prescription anti-nausea meds (talk to your doctor about what's safe at your stage) make a genuine difference and let them function way better. The secrecy part is stressful though, and I get that - but you might find things easier once you've told at least one trusted coworker. You don't owe anyone details, just "I'm dealing with something medical, it'll improve" is enough. That way you're not constantly stressed about hiding it, which honestly makes nausea worse. Give yourself permission to have rough days where you're less productive; this is temporary and your body's doing something intense.