On june i started to do exercise, and my period came to have a very slow flow not as strong as always, i started weight lifting on july and i received the same. i stopped and i still have the same problem. is that normal?

If you lost weight, that can affect periods. It would be prudent to see your gynecologist for an in-person evaluation. Get HPV vaccine. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines

Exercise and your weight lifting cause a lower amount of estrogen to be released, which results in a slower flow. After stopping it may take several months for a normal flow to return. Consult your OBGYN for advice.