Get a full blood hormonal panel done .
This could be hormonal why your getting the spots.
Acne can occur at any age. Androgens (male hormones found in male and female bodies) stimulate the sebaceous glands in the skin. Bacteria on the skin feed off this excess oil, called sebum, blocking the pores and leading to inflammed spots.
If oxytetracycline and doxycycline didn't work other antibiotics may help; lymecycline, erythromycin or minocycline. Alternatively, topical antibiotics (clindamycin, erythromycin) or topical retinoids (tretinoin, adapalene) may work.
Female acne patients can take an anti-androgen medicine called Spironolactone and/or an anti-androgen contraceptive pill such as Diane35 or Yasmin/Yaz.
Severe acne which does not respond to conventional treatments may warrant Oral Isotretinoin.
Unfortunately, you will have to avoid direct exposure to UV light (sun/sunbed) whilst using any of these medicines as severe sunburn or hyperpigmentation may occur.
Best Wishes, Eloise.