Welcome to HCM,
You haven't mentioned anything about your sexual activity.
Your symptoms other than loosing weight can normally occur prior to menstruation
as well as due to hot weather.
Menstrual blood when taking more time in coming out, can become brownish due to oxidation.
If ovulation is delayed due to any reason, period will also get delayed accordingly.
If you are not on dieting or performing excessive exercise, get your self evaluated by your physician, for loss of blood.
If your period is delayed for more than a week, do pregnancy
test (if sexually active) and consult your gynecologist if not active sexually.
Thanks for trusting Healthcaremagic and posting your query.
Hope you found my response to your query informative and helpful.
With good wishes,
Dr.Chandra Shekhar Sharma