Spotting After Period

Is it normal for a lady around the age of 21 to 23 to experience very light trace amounts of pink colored spotting when wiping? I had my period May 10th to the 16th like normal. Had sex with my fiancé on the 17th of May. He did cum inside me, which I'm fine with. I've been on Oral Contraceptives (The Pill) for the past three and a half years. Always taken it on time, every time. I switched brands after the first year of being on The Pill. But have stayed with the same one since then. I have been loosing weight due to health concerns for me. I saw my Nutrionist on May 4th and was told at that checkup I had lost over 15% of my body weight since I began working on weight management. Started seeing him as of January of this year. I read that there are multiple factors that can effect periods, cause spotting, abnormal bleeding, etc. however I am on a diet suppressant. I am taking 30mg Phentermine capsules twice a day, daily. They are from KVK Tech. They are half clear, half dark blue with K28 imprinted on them. With what looks like little balls inside the capsule. And I take my Pill every morning with the first Phentermine capsule of the day. The contraceptive I've been using is Chateal. They are Levonorgestrel and Ethinyl Estradiol Tablets, USP, 0.15mg/0.03mg which were manufactured by Famy Care Ltd. out of Sarigram - 396155, Gujarat, India for the company Afaxys, Inc. here in Charleston, SC, 29403, USA. So I'm wondering if I am experiencing this spotting abnormality due to the continuation of taking Phentermine twice daily, or if there is something else going on? I read that taking Phentermine for more than 12 weeks consecutively can have some damaging effects for the individual who is prescribed the drug. But I have been under a ton of stress due to finals for my college classes, arguments with my family, driving a lot and getting mad over it, and dealing with my fiancé getting dragged around by the USMC. Any possible ideas about what I could be experiencing would be greatly appreciated. I pay very close attention to how I feel, and what my body is exhibiting. Along with my health in general. Thank you.