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If the fingers had pre-cum or semen, and if you were during your fertile days/ovulation time at the time of sexual contact, chances of pregnancy are possible as suggested by changes in PMS and dysmenorrhea symptoms, along with lighter and shorter periods. Period pattern can also change due to changes in lifestyle, changes in stress levels, and changes in hormonal levels. Wait and watch for your next periods. Visit your doctor/gynecologist for further evaluation if periods do not start within 10 days, or if you get abnormal periods, or if you suspect chances of pregnancy, or if you develop any other new symptoms. If pregnancy gets ruled out, and if you are not ready for pregnancy, but intend to remain sexually active, you should consider visiting your gynecologist to get started on suitable regular birth control measures to be protected (after your periods). Be regular with birth control use as instructed. Avoid having unprotected sexual contact if you are not ready for pregnancy.
Take care.