Medication

So, probably have been mildly depressed for around the last 2 years or so, but in the last few months has worsened very quickly, can't get out of bed, can't function in normal life etc. Tried a new anti depressant (switched from Prozac, which I was previously taking for OCD, not depression) to Sertraline, but only 20mg a day so far. Been feeling more suicidal than I have ever before, but can't work out if this is a side effect of the new medication or just a natural progression of my life spiralling downwards. Anyone got any experience with side-effects/suicidal thoughts etc, anything is helpful as I don't really have anyone to talk to