Welcome Alex. If your left wing is falling that means that the plain stalled. So either you r trying to climb to hard or u r not using enough power, or both. Your speed should not go below 190 - 200 km/h on the bf. But generally you want to go as faster as you can in the BF.
when u get airborne, fly straight till u get 300 km/h. than start climbing at the rate that you can keep that speed.
cheers