Hello,
If an Ulceration lasts for more than one week , it is better to consult a dentist.
Ulceration which come and go, are usually called as Apthous ulcers. This usually occurs due to
vitamin deficiency / Stress etc.
Regarding the black spot , if you have any Amalgam filling ( Black Metal coloured filling )
there are chances of black discoloration of mucosa which is called " Amalgam tattoo" .
Other than that if u have a habit of smoking it can cause discoloration of mucosa.
Next Steps
With out clinical examination we cannot come to proper diagnosis , So it is advisable to consult a dentist.