A 2lb weight loss is definitely a big drop for a baby.
Has he taken to solids or is he a fussy eater? I can only advise to make sure he’s still taking enough breastmilk/formula in addition to his solids. If he has no food allergies, perhaps include higher calorie/fat foods such as cheeses, yoghurt, dried fruit purees, avocados, and maybe a few finger food snacks in between meals.
As a rule of thumb, most babies double their birth weight by 6 months, and triple their birth weight by 1 year. But you shouldn’t just focus on weight. How is his height growth, physical appearance and does he appear healthy, happy and active?
My son was a small baby at birth (only 6.3lbs) and has been consistently in the lower percentiles. He just turned 1 year and is now 18.8lbs but since he’s only 73cm his weight is good for his height. As expected, his weight gain has slowed down but I still weigh him regularly with my electronic scales at home just to make sure he doesn't lose any weight.
I hope everything goes well at the checkup.