Thanks for your question on Healthcare Magic.
I can understand your concern.
No need to worry for major heart or lung related diseases because your extensive work up for these diseases is normal.
Yes,
costochondritis can be the cause.
You should also get done
vitamin D3 and calcium levels because deficiency of these can cause similar kind of pain.
If deficiency then you may need supplements too.
For costochondritis, do following things for better symptomatic relief.
1. Avoid heavyweight lifting and strenuous exercise.
2. Avoid movements causing pain.
3. Avoid bad postures in sleep.
4. Take painkiller like
ibuprofen.
5. Apply warm water pad on affected areas.
Don't worry, you will be alright with all these.
Hope I have solved your query. I will be happy to help you further. Wish you good health. Thanks.