Hormone levels vary normally during the month and all of the hormones you mentioned hit rock bottom a few days before your menses. So it depends on when you have these tests done in relation to your cycle that determines if you have a problem. Chronic low levels of these hormones are usually only seen in low body fat athletes or women taking certain medications for established gynecologic issues.
FSH and LH are hormones produced by the pituitary that control release of hormones from the ovaries. They, per se don't affect gaining weight, but the hormones released, estradiol, progesterone and testosterone can have a profound effect in the distribution of fat and the creation and toning of muscles in the body. The process is complex, but the best is to have a good balance of hormones such as a youthful person to help you lose weight.