3 misscarriages

My husband and I have experienced two miscarriages and I personally have been thru 3.  My husband and I are trying to conceive but I'm not definite on when I'm ovulating.  When I take at home tests they read negative from days 14-18.  We went to a specialist and there isn't anything wrong with me.  They recommended trying days 10-21 to cover extra days. 
How do I find out when I'm ovulating?  
Any tests or something that worked for someone else?