A cold coming on only after eating oranges, and clearing up the day you stop, sounds like a sensitivity to citrus rather than a true infection. Pregnancy itself doesn't usually cause this kind of reaction.
Next Steps
You can skip oranges for now and get your
vitamin C from guava, amla, or other fruits that don't trigger it. Variety across fruits matters more than any single one.
Health Tips
If it happens with other foods too, or you notice throat tightness or breathing trouble, mention it to your obstetrician.