(When I was happy, I used to remember the all-powerful (Waheguru). So why did I get pain?

Amanpreet Kaur Ji Sukh Dukh is part of life. Guru says
ਸੂਖ ਦੂਖ ਇਸੁ ਮਨ ਕੀ ਬਿਰਥਾ ਤੁਝ ਹੀ ਆਗੈ ਸਾਰੈ ॥੧॥ AGGS 820
Sukh Dukh Es Mann Ki Birtha Tujh Hi Agai Sarai. ||1||
Suffering (Dukh) and Happiness (Sukh) are part of human life, our own making. Depending on our thinking or thoughts and the resulting actions, we experience Dukh or Sukh. If our thinking or thoughts and the resulting actions are primarily Dukh producing, then one cannot avoid Dukh. To the contrary, if our thinking or thoughts and the resulting actions are primarily Sukh producing, then we cannot avoid Sukh either. Accordingly, Gurbani reminds us that it’s foolishness to pray or ask God for only Sukh by abandoning all Dukh. We need to change our attitude towards life. If healthy life is a gift of God then illness is also gift of God. This body has to decay and getting illness is part of life. If we get miserable then our misery is going to increase. If we accept it as God’s Will (Hukam) then we will be happy even in illness and pain. Something which gives happiness to one person might give unhappiness to other. Rich people can be very unhappy and poor very happy if contented with whatever one has and try for more.
ਸੁਖੁ ਦੁਖੁ ਦੋਨੋ ਸਮ ਕਰਿ ਜਾਨੈ ਅਉਰੁ ਮਾਨੁ ਅਪਮਾਨਾ ॥ ਹਰਖ ਸੋਗ ਤੇ ਰਹੈ ਅਤੀਤਾ ਤਿਨਿ ਜਗਿ ਤਤੁ ਪਛਾਨਾ ॥੧॥ AGGS 219
Sukh Dukh Dono Sam Kar Janai Aor Maan Apamana || Harakh Sog Te Rehai Ateeta Tin Jag Tat Pachana ||1||
One who knows that sufferings and pleasure (Sukh Dukh), honour and dishonour are the same; who remains detached from joy and sorrow, realizes the true essence in the world.
ਨਰ ਚਾਹਤ ਕਛੁ ਅਉਰ ਅਉਰੈ ਕੀ ਅਉਰੈ ਭਈ ॥ ਚਿਤਵਤ ਰਹਿਓ ਠਗਉਰ ਨਾਨਕ ਫਾਸੀ ਗਲਿ ਪਰੀ ॥੩੮॥ AGGS 1428
Nar Chahat Kach Aur Aurai Ki Aurai Bhei || Chitvat Rehiou Thagour Nanak Fasi Gal Pari ||38||
ਜਤਨ ਬਹੁਤ ਸੁਖ ਕੇ ਕੀਏ ਦੁਖ ਕੋ ਕੀਓ ਨ ਕੋਇ ॥ ਕਹੁ ਨਾਨਕ ਸੁਨਿ ਰੇ ਮਨਾ ਹਰਿ ਭਾਵੈ ਸੋ ਹੋਇ ॥੩੯॥
Jatan Bahut Sukh Ke Keeae Dukh Ko Keeou N Koe || Kahu Nanak Sunn Re Mna Har Bhavai So Hoe ||39||
People wish for something, but something different happens. So their mind (Mann) is always at unease and unhappy. They then try different corrupt means of achieving and never come out of it. People make all sorts of efforts to find peace and pleasure, but no one tries to earn sufferings. (Sufferings and failure is an opportunity to learn and improve). Nanak says we should be contented and happy with what we are. At the same time strive for more and better life by honest means. We should make our suffering as an opportunity to learn and avoid it in future.
For example egg broken from outside force ends a life; if broken from inside force begins a new life. When suffering hits our mind (Mann) we then introspect and find fault with ourselves rather to an outside force. We then try to change ourselves and then a new person is born. If we are always indulged with worldly desires and feel superficial happiness, we will never try to learn to improve. Uncut diamond has less value but its value increases after it goes through the process of cutting (Sufferings). Suffering has to hit inside to change. That is ਦੁਖੁ ਦਾਰੂ ਸੁਖੁ ਰੋਗੁ ਭਇਆ ਜਾ ਸੁਖੁ ਤਾਮਿ ਨ ਹੋਈ (Dukh Daru Sukh Rog Bhaia Ja Sukh Taam N Hoi). Suffering (Dukh) acts as catalyst for quest of spiritual wisdom, which becomes the medicine for all our problems. More sufferings (Dukh) better spiritual wisdom.