As mentioned above, if you only have the low and not the high of mania, I would guess it i depression. I agree with the others, see a mental healthcare professional. Perhaps a prescription for antidepressants will help. I totally advise seeking help if you are contemplating suicide...it's not an option for you....your son needs his Mother and you can't deny him that. I hope you get help soon.
I have had the same problem since I was in 7th grade or so and I'm almost 31 now. I have a lot of trouble with suicidal thoughts and it is my husband and my kids and the thought of not seeing them anymore that stops me.
I would say see a psychiatrist and try to get some help for it.
It would depend on whether you also have any mood episodes that feel elevated that is in some way above normal. That of course would be mania. However a person can also have mixed states with the down aspect of depression but the sped up quality of mania. Only a psychiatrist could provide a conclusive diagnosis but you should keep a mood tracker and print out the results for them and if you have suicidal ideations on a regular basis it would be worthwhile to see one as soon as possible as all of this is very treatable.