brown spotting and back ache at 32 weeks, what does this mean ?

after wiping after going for a wee this morning I saw watery light brown blood on the paper :-/ Iv had lower back ache the last 2 days and last week I went in for a check as I had blurred vision and felt sick which was not normal for m . they did tests and said the baby was fine and that my symptoms were not pregnancy related so was fine to go home . I don't want to go back for a check if it's nothing but this is my second baby and never had bleeding for my first . Iv put a liner in to keep a eye on how much and if it changes colour but does anyone know what could have caused the spotting and back ache ? I read somewhere it happens in the days before birth ! surely it's to early for that ? advice please ...