Blocked nose at week 16

I am at my week 16 now and I’m getting blocked nose on one side constantly and I am constantly feeling like I cannot breathe, don’t have enough oxygen + it’s affecting my sleep. I’ve seen my gynae and was told I only can eat zyrtec 😢 any mums experience this at week16 where your nose is blocked??? Pls share remedies 😭😭😭