my first thought is... if you need to ask then the answer is always yes do the test. short version every human being has inside them their "gut instinct" and if the gut instinct is saying something is wrong or need to do a test or want to do a test then go i go with it and do it.

as far as the tests you can buy in a store .... they are not always reliable and are known for giving false negative and false positives. if you really want to know whether a child is yours or not the best thing to do is contact your local hospitals bloodwork lab and ask them if they do DNA testing. (most now days do because of family courts tend to need the results right away to decide things like custody, paternity/ maternity, child support, not to mention blood tissue typing when a baby is born.)

for DNA testing you will need an untainted, un manipulated, sanitary sample from both parents and the child in question.. usually hospitals do this with a special inside the cheek and mouth swabbing with a special "swab" and culture set.

the process is easy and my wife and I go through this with each of our children when they are born, because we are in a same sex marriage and if something happens to one we want the other to retain custody. just our way of completely avoiding any future problems for our children due to using IVF process and being in lesbian marriage. after the children are born, we all go through DNA testing, the biological father (same donor for each of our children) signs the paperwork and then which ever one of us (my wife or I) that was not the DNA of the child does the adoption process. this way everything is legal and done for our children in the event that something happens to one or the other of us. no battles over / for the children.

also you might want to check out your health insurance plans and the hospital where the child was born. sometimes DNA testing covered by insurance and is part of normal blood work panels for newborns.