Hi , everyone wants their acne to be gone faster and start picking on it, pls donot pick on it as treating acne is easier than treating acne scars which are stubborn.    Once someone picks on acne it ruptures with outburst of pus and most of the times comedones/ black heads too, in few cases comedones/black heads stays back to cause recurrence.    After rupture of acne it heals in days with pigmentation which we can post inflammatory hyperpigmentation. This is what happened in your case.    Applying lemon which has citric acid or garlic pastes can cause irritaion of skin causing more damage and hence one shud never use these home remedies.       Any case of acne can be simply treated by certain topical and/or oral medications and the pigmentation ,further tendency of acne can in additional addressed by chemical peels