Your child has little lower weight than of a child of his age and has good height for his age.  Weight gain is little slower after 1st year of life and that is absolutely normal.  About the triple phosphate crystals... That can be formed dye to dehydration or infection or by eating certain foods.  Given that his urine routine is not showing any signs of infection,  you can relax and increase his water intake.  No investigation is needed but you can get his urine test repeated again if u want. Bed wetting at night is considered normal for his age.  Picky eating and tantrums are normal at this age.

These crystals can be due to dehydration Make sure child is taking adequate amount of water U can do repeat urine test