What does it mean I’ve been super congested since 2 days ago with mostly clear but some yellow phlegm?

Not sure if I have a cold or allergies or both. I woke up super congested two days ago, to the point that I couldn’t breathe through my nose really at all. I’m almost 29, and I’ve never had spring allergies before. The first day, my throat hurt a lil bit (it’s hurt a LOT more every time I’ve had a cold in the past), but most of the discomfort was just sinus pressure from an extremely stuffy nose. I’ve been taking Claritin D twice a day since, and it’s definitely helped, though I’m still not back to normal yet, and the congestion is starting to make me hoarse now. On day one, my phlegm was white or clear, and it’s only been yellow when I blew my nose a few times in the middle of the night on day two. Otherwise, my phlegm color has been clear most of the time.

Yesterday I tested negative for covid and both strains of the flu. Seasonal allergy sufferers, does this description sound similar to your experience? Is it possible for adults to suddenly develop spring allergies in their late 20s?