On the basis of all information provided it looks like you are having some hormonal irregularity.
Most common reason in your age can be polycystic ovarian syndrome and endometriosis. Both of these conditions are diagnosed on the basis of ultrasound .So now you need to make one appointment for assessment by your OB /Gynae doctor.
Please ask if you have any more querries.
Yes ,not necessarily it is with painful periods.
Iron deficiency can be one reason to consider.
This can be tested by blood hemoglobin levels.
We can talk in detail if you like.
Yes ,you are right.As we were discussing that iron deficiency can be one reason.
So you can try taking some over the counter iron medicines.
Also eat more fruits like apples and green leafy vegetables.
Some time it helps with this situation.