prior to trying I had normal cycles?

Hi,
Welcome to ehealthforum,
Shorter and lighter periods along with weight gain and spotting could be suggestive of possibility of pregnancy. The urine pregnancy test (UPT) kits are calibrated ones, so unless the hormone levels in urine reach a certain level, they do not show positive results. They can also show false negative results during early pregnancy. Blood/serum HCG level estimation is accurate. UPT should always be done on early morning first urine sample as the concentration of pregnancy hormone HCG is believed to be highest in this sample. You can consider repeating UPT on early morning sample to see if it turns positive. Look out for development of any other new symptoms suggestive of early pregnancy if you suspect to be pregnant. If pregnancy is suspected, consider visiting your doctor/gynecologist at the earliest for further examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). If pregnancy gets confirmed, get ultrasound scan done to confirm the gestational age. Take adequate rest. Drink plenty of water. Maintain healthy diet.
Take care.