I get it OP, and you have my sympathies. I had that with my first. I'd joined a new team, a very unsympathetic groupwho made me feel ten times worse, let alone all the pressure I was putting on myself .
No, pregnancy is not an illness. But it can present with symptoms that are debilitating, just like an illness. If something is making you unwell, that's good enough for me to describe it as illness.
Some women sail through pregnancy, others feel a tiny bit nauseous for an hour a day for two or three weeks. Yet others struggle dreadfully with horrible relentless sickness, or SPD, or gestational diabetes, or any number of complications. I found, sadly, women from the first two groups were often the quickest to judge - having had straightforward pregnancies they assumed i must have been making a fuss.
So I had a frank conversation where I explained I had been constantly nauseous and vomiting for twenty weeks, that I hadn't had a proper meal in that time, that I couldn't always keep the anti sickness meds down, that I constantly felt like I was on a listing boat, that I was dehydrated and had had to go on a drip. I said it was not the same thing as feeling ropy for an hour in the morning and having to have a ginger biscuit. and I was ready to stab the next person who said 'ooh have you tried ginger biscuits'
Fuck 'pregnancy is not an illness'. Have courage in your convictions and remember a lot of people still don't fully understand how bad it can be. Your HR department will though, I'm sure of it.