It's a common misconception that a lot of sex will stretch your vagina out. The vagina is very flexible and has no problem being stretched and bouncing back from your average sexual encounter. So not having sex for a week would not make your vagina tighter.
"Giving birth can cause your vagina to stretch out; having sex can't."
http://www.cosmopolitan.com/sex-love/advic
e/questions/vagina-muscle.
Your vagina does get tighter and looser at different times though, it's just not due to having sex or not having sex.
Things that can effect how tight or loose you seem:
"1. Women's vaginas are less elastic when they are not sexually aroused. They become more elastic — "looser" — the more sexually excited they become. A woman may feel "tighter" to a man when she is less aroused, less comfortable, and having less pleasure than her partner.
2. Hormonal shifts during a woman's menstrual cycle affect vaginal secretions and may affect vaginal elasticity. She may feel "looser" on certain days of her cycle than on others.
3. Certain drugs, such as antihistamines or marijuana, may make the walls of the vagina feel dry so they seem "tighter."
4. A woman's vagina may feel tighter or looser in different positions for intercourse."
http://www.plannedparenthood.org/sexual-he
alth/ask-dr-cullins/ask-dr-cullins-relatio
nships-5287.htm
So you can try kegels. I don't bother with them, so I can't give you first hand experience there. Just be aware of reproductive anatomy and the fact that having sex is not making your vagina huge or loose, just like abstaining from sex is not going to make your vagina small and tight. It sounds like you just get in the mood and well lubricated. That makes the penis slide in and out a lot easier, which protects the inside of your vagina from rips and tears, but it can also decrease some feeling.