Questions & Answers about Bacağım ağrıyor.
It is:
- bacak = leg
- -ım = my
So:
- bacak + ım → bacağım = my leg
The final form changes a little because of a sound change in Turkish, which is why you do not see bacakım.
This is a very common Turkish sound change.
When some nouns ending in -k take a suffix that begins with a vowel, the k often softens to ğ.
So:
- bacak
- -ım → bacağım
This kind of change is normal in Turkish and happens in many words. It is not a special irregularity of this sentence.