considering the fact that most scenarios where Jesus healed people,he said to them afterwards to go and sin no more. Is it apts to conclude that sicknesses and diseases people are facing were brought upon them due to their sinful acts?

Yes sin do open doors of affliction on people but it's not a general thing . Some affliction comes medically or naturally some comes as attack of the enemy .and Some come for Gods glory .

John 9:2-3
And his disciples asked him, saying, Master, who did sin, this man, or his parents, that he was born blind? Jesus answered, Neither hath this man sinned, nor his parents: but that the works of God should be made manifest in him.

Joagbaje:
Yes sin do open doors of affliction on people but it's not a general thing . Some affliction comes medically or naturally some comes as attack of the enemy .and Some come for Gods glory .

John 9:2-3
And his disciples asked him, saying, Master, who did sin, this man, or his parents, that he was born blind? Jesus answered, Neither hath this man sinned, nor his parents: but that the works of God should be made manifest in him.

since this was before Jesus' death is it still amenable after his death?

Your conclusion that in most of Jesus healings he refered to sin as the root cause is not entirely correct.

Jesus only made reference to sin in two cases:

1) A man sick of palsy. Matt. 9:2; Mark 2:5; Luke 5:20.

2) The man at the pool of Bethesda. John 5:2-14.

I cannot remember any other instance. Personally I don't think two should be tagged most in this case.

However, sin and sickness are bed fellows according to Deut. 28:60-61

Deuteronomy: 28. 60. Moreover he will bring upon thee all the diseases of Egypt, which thou wast afraid of; and they shall cleave unto thee.

61. Also every sickness, and every plague, which is not written in the book of this law, them will the LORD bring upon thee, until thou be destroyed.