Welcome to HCM.
Periods may be delayed due to polycystic ovaries
Since you are chubby the possibility of polycystic ovaries is all the more likely.
Patients with polycystic ovaries may have one or more of the following :
1 > irregular periods
2 > over weight ( obesity)
3 > excess of hair growth in unwanted places ( Hirsutism
You will need an ultra sound
scan to exclude or confirm polycystic ovaries.
By the way Negative PT does not exclude pregnancy
but only indicates that the pregnancy is not of the duration which can be picked up by the particular test kit.
Wish you all the best.