I went to see my cusins newborn baby and i had thoughts of killing it,im 15 with clinical depression?

because i feel like i have someone in my head urging me to do anything it wants

Homicidal thoughts are common for teens, study says
Have you ever thought about killing someone? Raise your hand if you have.

Well, guess what? Just about all the hands go up. Mine too.

It appears that homicidal ideation is a relatively common phenomena. According to a study, 91% of men and 84% of women have had at least one vivid homicidal fantasy in their lifetime. For many, more than one. A part of Buss's research involved interviewing people about these homicidal fantasies detailing their content and the events that precipitated them. The findings are interesting. To start, you might ask yourself why you have ever had one of these fantasies.

Now the ethical status of homicidal fantasies seems pretty clear. You shouldn't have them. You shouldn't indulge them. Agreed. So, why dwell on the topic? Because the content of the homicidal fantasies reveals a lot about human nature.

sex and homicidal impulses are intimately related. This finding is confirmed by homicide statistics. For example, one study, looking at the murders in Dayton, Ohio during a five year period, found that 52% of the women murdered were murdered by either a male lover, boyfriend, or husband.

Homicidal thoughts are common for teens, study says
Nearly half the adolescents sampled in a recent study said they had fantasized about committing homicide.

If evolution shaped human nature to be an aggressive sort of nature, we should own up to this legacy...because most of the homicidal fantasies reported in this study involved weapons, and because those weapons were rated as being lethal and easy to use, and were available to most fantasizers, the logical target for policy can only be the tools [weapons] that make killing a behavioral option--even for 6-year-old children."

FDA (Food and Drug Administration: Anti-depressants can cause homicidal thoughts...........An antidepressant that Andrea Yates had been taking before she drowned her five children in 2001 has recently been found to possibly increase the risk of homicidal thoughts, according to a medical watchdog group.Obviously this is a severely mentally ill individual who was on a plethora of psychiatric meds,"...... said. "There's no question mental illness killed those children."

Anti-depressants can cause homicidal thoughts are you taking any drug.?Homicidal Thoughts are Among some Antidepressant's Side Effects.

Consult your doctor ASAp

Don't worry. I have had these thoughts. In fact they are very common among the severely depressed/anxious. This is a symptom of neurosis. You saw the baby and immediately realised how terrible and frightening it would be to harm it. You became so obsessed by this thought that you worried you might go through with it. Disturbing obsessions and thoughts are very common among people with mental health problems. A therapist of mine once told me she had treated a woman who was terrified because she couldn't stop thinking about killing her own child but didn't want to.
This only applies if the thoughts frighten you. Are you afraid of doing it? If your thoughts have the opposite effect - you are excited by the idea - you may have psychosis rather than neurosis and should see a doctor immediately.
Otherwise I can assure you you're not going to do it. The fear will pass. But you should still try to see a therapist. I am a big advocate of CBT. Ask your doctor about this approach.
Good luck.

Ok... wow.
Why did you feel like killing it?
Thats concering.
Really think about it.
What would you gain by killing it?
What would EVERYONE around you loose? A LOT!
Think about it!

You better talk to someone like a pyscologist you def need it, there is no way around it, sorry