trying to get pregnent

I am 27 years old and have been trying to get pregnent for two years. I have a 6 year old son and my husband has 3 children from a preveous marrage. I was 5 foot 6 and 210 pounds and was not haveing my period verry often, probibly once every 3 or 4 months.  4 months ago I lost 12 pounds and have been haveing my period about once a month. This last time my period lasted 10 days and one week latter I am spotting again (brown to light red spotting).
Is this a sign that something may be causeing me to have infertility problems.